unattended-upgrades runs twice every day but never installs anything

Upon logging in to system it is clear that a large number of upgrades are available:

258 packages can be updated.
117 updates are security updates.

Output from sudo apt full-upgrade confirms it:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
  libllvm3.8 libllvm3.8:i386 libmircommon5 linux-headers-4.4.0-65 linux-headers-4.4.0-65-generic
  linux-headers-4.4.0-66 linux-headers-4.4.0-66-generic linux-headers-4.4.0-70 linux-headers-4.4.0-70-generic
  linux-headers-4.4.0-71 linux-headers-4.4.0-71-generic linux-headers-4.4.0-72 linux-headers-4.4.0-72-generic
  linux-headers-4.4.0-75 linux-headers-4.4.0-75-generic linux-headers-4.4.0-77 linux-headers-4.4.0-77-generic
  linux-headers-4.4.0-78 linux-headers-4.4.0-78-generic linux-headers-4.4.0-79 linux-headers-4.4.0-79-generic
  linux-headers-4.4.0-81 linux-headers-4.4.0-81-generic linux-headers-4.4.0-83 linux-headers-4.4.0-83-generic
  linux-headers-4.4.0-87 linux-headers-4.4.0-87-generic linux-headers-4.4.0-89 linux-headers-4.4.0-89-generic
  linux-image-4.4.0-65-generic linux-image-4.4.0-66-generic linux-image-4.4.0-70-generic
  linux-image-4.4.0-71-generic linux-image-4.4.0-72-generic linux-image-4.4.0-75-generic
  linux-image-4.4.0-77-generic linux-image-4.4.0-78-generic linux-image-4.4.0-79-generic
  linux-image-4.4.0-81-generic linux-image-4.4.0-83-generic linux-image-4.4.0-87-generic
  linux-image-4.4.0-89-generic linux-image-extra-4.4.0-65-generic linux-image-extra-4.4.0-66-generic
  linux-image-extra-4.4.0-70-generic linux-image-extra-4.4.0-71-generic linux-image-extra-4.4.0-72-generic
  linux-image-extra-4.4.0-75-generic linux-image-extra-4.4.0-77-generic linux-image-extra-4.4.0-78-generic
  linux-image-extra-4.4.0-79-generic linux-image-extra-4.4.0-81-generic linux-image-extra-4.4.0-83-generic
  linux-image-extra-4.4.0-87-generic linux-image-extra-4.4.0-89-generic linux-signed-image-4.4.0-65-generic
  linux-signed-image-4.4.0-66-generic linux-signed-image-4.4.0-70-generic linux-signed-image-4.4.0-71-generic
  linux-signed-image-4.4.0-72-generic linux-signed-image-4.4.0-75-generic linux-signed-image-4.4.0-77-generic
  linux-signed-image-4.4.0-78-generic linux-signed-image-4.4.0-79-generic linux-signed-image-4.4.0-81-generic
  linux-signed-image-4.4.0-83-generic linux-signed-image-4.4.0-87-generic linux-signed-image-4.4.0-89-generic
  snap-confine ubuntu-core-launcher
Use 'sudo apt autoremove' to remove them.
The following NEW packages will be installed
  linux-headers-4.4.0-98 linux-headers-4.4.0-98-generic linux-image-4.4.0-98-generic
  linux-image-extra-4.4.0-98-generic linux-signed-image-4.4.0-98-generic
The following packages will be upgraded:
  apparmor apport apport-gtk apport-retrace bind9-host binutils bluez bluez-cups bluez-obexd ca-certificates cpp-5
  cracklib-runtime crash cryptsetup-bin cups cups-bsd cups-client cups-common cups-core-drivers cups-daemon
  cups-ppdc cups-server-common debootstrap distro-info-data dnsmasq-base dnsutils evince evince-common firefox
  firefox-locale-en flashplugin-installer g++-5 gcc-5 gcc-5-base gcc-5-base:i386 ghostscript ghostscript-x
  gir1.2-gdkpixbuf-2.0 gir1.2-javascriptcoregtk-4.0 gir1.2-packagekitglib-1.0 gir1.2-webkit2-4.0 git git-man
  gnome-software gnome-software-common grub-common grub-efi-amd64 grub-efi-amd64-bin grub-efi-amd64-signed
  grub2-common gvfs gvfs-backends gvfs-bin gvfs-common gvfs-daemons gvfs-fuse gvfs-libs initramfs-tools
  initramfs-tools-bin initramfs-tools-core iproute iproute2 libapparmor-perl libapparmor1 libasan2 libatomic1
  libbind9-140 libbluetooth3 libcc1-0 libcilkrts5 libcrack2 libcryptsetup4 libcups2 libcups2:i386 libcupscgi1
  libcupsimage2 libcupsmime1 libcupsppdc1 libcurl3 libcurl3-gnutls libdns-export162 libdns162 libegl1-mesa
  libevdocument3-4 libevview3-3 libgbm1 libgcc-5-dev libgd3 libgd3:i386 libgdk-pixbuf2.0-0 libgdk-pixbuf2.0-common
  libgfortran3 libgl1-mesa-dri libgl1-mesa-dri:i386 libgl1-mesa-glx libgl1-mesa-glx:i386 libglapi-mesa
  libglapi-mesa:i386 libgles2-mesa libgnutls-openssl27 libgnutls30 libgnutls30:i386 libgomp1 libgraphite2-3 libgs9
  libgs9-common libicu55 libicu55:i386 libidn11 libidn11:i386 libisc-export160 libisc160 libisccc140 libisccfg140
  libitm1 libjavascriptcoregtk-4.0-18 liblouis-data liblouis9 liblsan0 liblwres141 libmirclient9 libmircommon7
  libmircore1 libmirprotobuf3 libmpx0 libmysqlclient20:i386 libnm-gtk-common libnm-gtk0 libnma-common libnma0
  libnss-winbind libnss3 libnss3-1d libnss3-nssdb libosmesa6 libosmesa6:i386 libpackagekit-glib2-16 libpam-systemd
  libpam-winbind libperl5.22 libplist3 libplymouth4 libpoppler-glib8 libpoppler58 libpulse-mainloop-glib0 libpulse0
  libpulse0:i386 libpulsedsp libpython3.5 libpython3.5-minimal libpython3.5-stdlib libquadmath0 libsmbclient
  libsnapd-glib1 libssl-dev libssl-doc libssl1.0.0 libssl1.0.0:i386 libstdc++-5-dev libstdc++6 libstdc++6:i386
  libsystemd0 libsystemd0:i386 libtsan0 libubsan0 libudev-dev libudev1 libudev1:i386 libwayland-client0
  libwayland-cursor0 libwayland-egl1-mesa libwayland-server0 libwbclient0 libwebkit2gtk-4.0-37
  libwebkit2gtk-4.0-37-gtk2 libxatracker2 libxfont1 libxml2 libxml2:i386 libxml2-utils linux-firmware linux-generic
  linux-headers-generic linux-image-generic linux-libc-dev linux-signed-generic linux-signed-image-generic
  logrotate lshw makedumpfile mesa-vdpau-drivers mysql-common network-manager-gnome ntpdate openssl perl perl-base
  perl-modules-5.22 plymouth plymouth-label plymouth-theme-ubuntu-logo plymouth-theme-ubuntu-text poppler-utils
  postfix pulseaudio pulseaudio-module-bluetooth pulseaudio-module-x11 pulseaudio-utils python-apport python-jwt
  python-libxml2 python-problem-report python-samba python3-apport python3-distupgrade python3-jwt python3-louis
  python3-problem-report python3-update-manager python3.5 python3.5-minimal qemu-user-static resolvconf samba
  samba-common samba-common-bin samba-dsdb-modules samba-libs samba-vfs-modules smbclient snap-confine snapd
  snapd-login-service systemd systemd-sysv tcpdump texlive-base texlive-fonts-recommended
  texlive-generic-recommended texlive-latex-base texlive-latex-recommended thunderbird thunderbird-gnome-support
  thunderbird-locale-en thunderbird-locale-en-gb thunderbird-locale-en-us tzdata ubuntu-core-launcher
  ubuntu-desktop ubuntu-drivers-common ubuntu-minimal ubuntu-release-upgrader-core ubuntu-release-upgrader-gtk
  ubuntu-software ubuntu-standard udev update-manager update-manager-core update-notifier update-notifier-common
  wget winbind wpasupplicant xserver-common xserver-xorg-core xul-ext-ubufox
266 to upgrade, 5 to newly install, 0 to remove and 0 not to upgrade.
Need to get 95.1 MB/427 MB of archives.
After this operation, 368 MB of additional disk space will be used.
Do you want to continue? [Y/n] n

Unattended upgrade is running roughly every two days, as shown by the contents of /var/log/unattended-upgrades/unattended-upgrades.log:

2017-11-10 19:11:17,755 INFO Initial blacklisted packages: 
2017-11-10 19:11:17,756 INFO Initial whitelisted packages: 
2017-11-10 19:11:17,756 INFO Starting unattended upgrades script
2017-11-10 19:11:17,756 INFO Allowed origins are: ['o=Ubuntu,a=xenial', 'o=Ubuntu,a=xenial-security', 'o=UbuntuESM,a=xenial']
2017-11-11 14:10:07,827 INFO Initial blacklisted packages: 
2017-11-11 14:10:07,828 INFO Initial whitelisted packages: 
2017-11-11 14:10:07,828 INFO Starting unattended upgrades script
2017-11-11 14:10:07,828 INFO Allowed origins are: ['o=Ubuntu,a=xenial', 'o=Ubuntu,a=xenial-security', 'o=UbuntuESM,a=xenial']
2017-11-14 00:07:21,327 INFO Initial blacklisted packages: 
2017-11-14 00:07:21,328 INFO Initial whitelisted packages: 
2017-11-14 00:07:21,328 INFO Starting unattended upgrades script
2017-11-14 00:07:21,328 INFO Allowed origins are: ['o=Ubuntu,a=xenial', 'o=Ubuntu,a=xenial-security', 'o=UbuntuESM,a=xenial']
2017-11-16 18:47:23,067 INFO Initial blacklisted packages: 
2017-11-16 18:47:23,067 INFO Initial whitelisted packages: 
2017-11-16 18:47:23,067 INFO Starting unattended upgrades script
2017-11-16 18:47:23,068 INFO Allowed origins are: ['o=Ubuntu,a=xenial', 'o=Ubuntu,a=xenial-security', 'o=UbuntuESM,a=xenial']
2017-11-17 12:08:29,321 INFO Initial blacklisted packages: 
2017-11-17 12:08:29,321 INFO Initial whitelisted packages: 
2017-11-17 12:08:29,322 INFO Starting unattended upgrades script
2017-11-17 12:08:29,322 INFO Allowed origins are: ['o=Ubuntu,a=xenial', 'o=Ubuntu,a=xenial-security', 'o=UbuntuESM,a=xenial']

The output from sudo unattended-upgrades --dry-run shows that unattended-upgrades is aware that it needs to install updated packages:

Extract templates from packages: 100%
Preconfiguring packages ...
/usr/bin/dpkg --status-fd 9 --unpack --auto-deconfigure /var/cache/apt/archives/libperl5.22_5.22.1-9ubuntu0.2_amd64.deb /var/cache/apt/archives/perl_5.22.1-9ubuntu0.2_amd64.deb /var/cache/apt/archives/perl-base_5.22.1-9ubuntu0.2_amd64.deb 
/usr/bin/dpkg --status-fd 11 --configure perl-base:amd64 
/usr/bin/dpkg --status-fd 13 --unpack --auto-deconfigure /var/cache/apt/archives/perl-modules-5.22_5.22.1-9ubuntu0.2_all.deb /var/cache/apt/archives/samba-dsdb-modules_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/libnss-winbind_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/libpam-winbind_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/winbind_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/samba_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/samba-common-bin_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/smbclient_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/python-samba_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/samba-vfs-modules_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/samba-libs_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/libwbclient0_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/libsmbclient_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_amd64.deb /var/cache/apt/archives/samba-common_2%3a4.3.11+dfsg-0ubuntu0.16.04.11_all.deb /var/cache/apt/archives/tzdata_2017c-0ubuntu0.16.04_all.deb /var/cache/apt/archives/libisc-export160_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libdns-export162_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libidn11_1.32-3ubuntu1.2_amd64.deb /var/cache/apt/archives/libidn11_1.32-3ubuntu1.2_i386.deb /var/cache/apt/archives/libssl-doc_1.0.2g-1ubuntu4.9_all.deb /var/cache/apt/archives/libssl-dev_1.0.2g-1ubuntu4.9_amd64.deb /var/cache/apt/archives/libssl1.0.0_1.0.2g-1ubuntu4.9_i386.deb /var/cache/apt/archives/libssl1.0.0_1.0.2g-1ubuntu4.9_amd64.deb /var/cache/apt/archives/libicu55_55.1-7ubuntu0.3_i386.deb /var/cache/apt/archives/libicu55_55.1-7ubuntu0.3_amd64.deb /var/cache/apt/archives/libxml2_2.9.3+dfsg1-1ubuntu0.3_amd64.deb /var/cache/apt/archives/libxml2_2.9.3+dfsg1-1ubuntu0.3_i386.deb /var/cache/apt/archives/bind9-host_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/dnsutils_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libisc160_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libdns162_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libisccc140_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libisccfg140_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/liblwres141_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/libbind9-140_1%3a9.10.3.dfsg.P4-8ubuntu1.8_amd64.deb /var/cache/apt/archives/openssl_1.0.2g-1ubuntu4.9_amd64.deb /var/cache/apt/archives/ca-certificates_20170717~16.04.1_all.deb /var/cache/apt/archives/libcurl3-gnutls_7.47.0-1ubuntu2.4_amd64.deb /var/cache/apt/archives/tcpdump_4.9.2-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/wget_1.17.1-1ubuntu1.3_amd64.deb /var/cache/apt/archives/python3-problem-report_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/python3-apport_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/apport_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/apport-gtk_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/python-problem-report_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/python-apport_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/apport-retrace_2.20.1-0ubuntu2.12_all.deb /var/cache/apt/archives/bluez_5.37-0ubuntu5.1_amd64.deb /var/cache/apt/archives/bluez-cups_5.37-0ubuntu5.1_amd64.deb /var/cache/apt/archives/bluez-obexd_5.37-0ubuntu5.1_amd64.deb /var/cache/apt/archives/dnsmasq-base_2.75-1ubuntu0.16.04.3_amd64.deb /var/cache/apt/archives/libgdk-pixbuf2.0-0_2.32.2-1ubuntu1.3_amd64.deb /var/cache/apt/archives/libgdk-pixbuf2.0-common_2.32.2-1ubuntu1.3_all.deb /var/cache/apt/archives/firefox_57.0+build4-0ubuntu0.16.04.5_amd64.deb /var/cache/apt/archives/firefox-locale-en_57.0+build4-0ubuntu0.16.04.5_amd64.deb /var/cache/apt/archives/libnss3-nssdb_2%3a3.28.4-0ubuntu0.16.04.3_all.deb /var/cache/apt/archives/libnss3-1d_2%3a3.28.4-0ubuntu0.16.04.3_amd64.deb /var/cache/apt/archives/libnss3_2%3a3.28.4-0ubuntu0.16.04.3_amd64.deb /var/cache/apt/archives/libcurl3_7.47.0-1ubuntu2.4_amd64.deb /var/cache/apt/archives/flashplugin-installer_27.0.0.187ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/ghostscript_9.18~dfsg~0-0ubuntu2.7_amd64.deb /var/cache/apt/archives/ghostscript-x_9.18~dfsg~0-0ubuntu2.7_amd64.deb /var/cache/apt/archives/libgs9-common_9.18~dfsg~0-0ubuntu2.7_all.deb /var/cache/apt/archives/libgs9_9.18~dfsg~0-0ubuntu2.7_amd64.deb /var/cache/apt/archives/gir1.2-gdkpixbuf-2.0_2.32.2-1ubuntu1.3_amd64.deb /var/cache/apt/archives/libwebkit2gtk-4.0-37-gtk2_2.18.3-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/libwebkit2gtk-4.0-37_2.18.3-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/libjavascriptcoregtk-4.0-18_2.18.3-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/libwayland-client0_1.12.0-1~ubuntu16.04.2_amd64.deb /var/cache/apt/archives/libwayland-server0_1.12.0-1~ubuntu16.04.2_amd64.deb /var/cache/apt/archives/gir1.2-webkit2-4.0_2.18.3-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/gir1.2-javascriptcoregtk-4.0_2.18.3-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/git-man_1%3a2.7.4-0ubuntu1.3_all.deb /var/cache/apt/archives/git_1%3a2.7.4-0ubuntu1.3_amd64.deb /var/cache/apt/archives/libbluetooth3_5.37-0ubuntu5.1_amd64.deb /var/cache/apt/archives/libgd3_2.1.1-4ubuntu0.16.04.8_amd64.deb /var/cache/apt/archives/libgd3_2.1.1-4ubuntu0.16.04.8_i386.deb /var/cache/apt/archives/libgraphite2-3_1.3.10-0ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/libmircore1_0.26.3+16.04.20170605-0ubuntu1.1_amd64.deb /var/cache/apt/archives/libmircommon7_0.26.3+16.04.20170605-0ubuntu1.1_amd64.deb /var/cache/apt/archives/libmirprotobuf3_0.26.3+16.04.20170605-0ubuntu1.1_amd64.deb /var/cache/apt/archives/libmirclient9_0.26.3+16.04.20170605-0ubuntu1.1_amd64.deb /var/cache/apt/archives/mysql-common_5.7.20-0ubuntu0.16.04.1_all.deb /var/cache/apt/archives/libmysqlclient20_5.7.20-0ubuntu0.16.04.1_i386.deb /var/cache/apt/archives/libplist3_1.12-3.1ubuntu0.16.04.1_amd64.deb /var/cache/apt/archives/libpoppler58_0.41.0-0ubuntu1.5_amd64.deb /var/cache/apt/archives/libpoppler-glib8_0.41.0-0ubuntu1.5_amd64.deb /var/cache/apt/archives/libwayland-cursor0_1.12.0-1~ubuntu16.04.2_amd64.deb /var/cache/apt/archives/libxfont1_1%3a1.5.1-1ubuntu0.16.04.3_amd64.deb /var/cache/apt/archives/libxml2-utils_2.9.3+dfsg1-1ubuntu0.3_amd64.deb /var/cache/apt/archives/linux-firmware_1.157.13_all.deb /var/cache/apt/archives/linux-image-4.4.0-98-generic_4.4.0-98.121_amd64.deb /var/cache/apt/archives/linux-image-extra-4.4.0-98-generic_4.4.0-98.121_amd64.deb /var/cache/apt/archives/linux-generic_4.4.0.98.103_amd64.deb /var/cache/apt/archives/linux-image-generic_4.4.0.98.103_amd64.deb /var/cache/apt/archives/linux-signed-image-4.4.0-98-generic_4.4.0-98.121_amd64.deb /var/cache/apt/archives/linux-signed-generic_4.4.0.98.103_amd64.deb /var/cache/apt/archives/linux-signed-image-generic_4.4.0.98.103_amd64.deb /var/cache/apt/archives/linux-headers-4.4.0-98_4.4.0-98.121_all.deb /var/cache/apt/archives/linux-headers-4.4.0-98-generic_4.4.0-98.121_amd64.deb /var/cache/apt/archives/linux-headers-generic_4.4.0.98.103_amd64.deb /var/cache/apt/archives/linux-libc-dev_4.4.0-98.121_amd64.deb /var/cache/apt/archives/poppler-utils_0.41.0-0ubuntu1.5_amd64.deb /var/cache/apt/archives/python-jwt_1.3.0-1ubuntu0.1_all.deb /var/cache/apt/archives/python-libxml2_2.9.3+dfsg1-1ubuntu0.3_amd64.deb /var/cache/apt/archives/python3-jwt_1.3.0-1ubuntu0.1_all.deb /var/cache/apt/archives/qemu-user-static_1%3a2.5+dfsg-5ubuntu10.16_amd64.deb /var/cache/apt/archives/texlive-fonts-recommended_2015.20160320-1ubuntu0.1_all.deb /var/cache/apt/archives/texlive-latex-base_2015.20160320-1ubuntu0.1_all.deb /var/cache/apt/archives/texlive-latex-recommended_2015.20160320-1ubuntu0.1_all.deb /var/cache/apt/archives/texlive-generic-recommended_2015.20160320-1ubuntu0.1_all.deb /var/cache/apt/archives/texlive-base_2015.20160320-1ubuntu0.1_all.deb /var/cache/apt/archives/thunderbird-locale-en_1%3a52.4.0+build1-0ubuntu0.16.04.2_amd64.deb /var/cache/apt/archives/thunderbird_1%3a52.4.0+build1-0ubuntu0.16.04.2_amd64.deb /var/cache/apt/archives/thunderbird-gnome-support_1%3a52.4.0+build1-0ubuntu0.16.04.2_amd64.deb /var/cache/apt/archives/thunderbird-locale-en-gb_1%3a52.4.0+build1-0ubuntu0.16.04.2_all.deb /var/cache/apt/archives/thunderbird-locale-en-us_1%3a52.4.0+build1-0ubuntu0.16.04.2_all.deb /var/cache/apt/archives/wpasupplicant_2.4-0ubuntu6.2_amd64.deb /var/cache/apt/archives/xserver-common_2%3a1.18.4-0ubuntu0.7_all.deb /var/cache/apt/archives/xserver-xorg-core_2%3a1.18.4-0ubuntu0.7_amd64.deb /var/cache/apt/archives/xul-ext-ubufox_3.4-0ubuntu0.16.04.2_all.deb /var/cache/apt/archives/liblouis-data_2.6.4-2ubuntu0.1_all.deb /var/cache/apt/archives/liblouis9_2.6.4-2ubuntu0.1_amd64.deb /var/cache/apt/archives/python3-louis_2.6.4-2ubuntu0.1_all.deb 
/usr/bin/dpkg --status-fd 15 --configure perl-modules-5.22:all libperl5.22:amd64 perl:amd64 libwbclient0:amd64 samba-libs:amd64 samba-dsdb-modules:amd64 samba-common:all python-samba:amd64 samba-common-bin:amd64 samba:amd64 winbind:amd64 libnss-winbind:amd64 libpam-winbind:amd64 libsmbclient:amd64 smbclient:amd64 samba-vfs-modules:amd64 tzdata:all libisc-export160:amd64 libdns-export162:amd64 libidn11:i386 libidn11:amd64 libssl-doc:all libssl1.0.0:amd64 libssl1.0.0:i386 libssl-dev:amd64 libicu55:amd64 libicu55:i386 libxml2:i386 libxml2:amd64 libisc160:amd64 libdns162:amd64 libisccc140:amd64 libisccfg140:amd64 libbind9-140:amd64 liblwres141:amd64 bind9-host:amd64 dnsutils:amd64 openssl:amd64 ca-certificates:all libcurl3-gnutls:amd64 tcpdump:amd64 wget:amd64 python3-problem-report:all python3-apport:all apport:all apport-gtk:all python-problem-report:all python-apport:all apport-retrace:all bluez:amd64 bluez-cups:amd64 bluez-obexd:amd64 dnsmasq-base:amd64 libgdk-pixbuf2.0-common:all libgdk-pixbuf2.0-0:amd64 firefox:amd64 firefox-locale-en:amd64 libnss3-nssdb:all libnss3:amd64 libnss3-1d:amd64 libcurl3:amd64 flashplugin-installer:amd64 libgs9-common:all libgs9:amd64 ghostscript:amd64 ghostscript-x:amd64 gir1.2-gdkpixbuf-2.0:amd64 libjavascriptcoregtk-4.0-18:amd64 libwayland-client0:amd64 libwayland-server0:amd64 libwebkit2gtk-4.0-37:amd64 libwebkit2gtk-4.0-37-gtk2:amd64 gir1.2-javascriptcoregtk-4.0:amd64 gir1.2-webkit2-4.0:amd64 git-man:all git:amd64 libbluetooth3:amd64 libgd3:i386 libgd3:amd64 libgraphite2-3:amd64 libmircore1:amd64 libmircommon7:amd64 libmirprotobuf3:amd64 libmirclient9:amd64 mysql-common:all libmysqlclient20:i386 libplist3:amd64 libpoppler58:amd64 libpoppler-glib8:amd64 libwayland-cursor0:amd64 libxfont1:amd64 libxml2-utils:amd64 linux-firmware:all linux-image-4.4.0-98-generic:amd64 linux-image-extra-4.4.0-98-generic:amd64 linux-image-generic:amd64 linux-headers-4.4.0-98:all linux-headers-4.4.0-98-generic:amd64 linux-headers-generic:amd64 linux-generic:amd64 linux-signed-image-4.4.0-98-generic:amd64 linux-signed-image-generic:amd64 linux-signed-generic:amd64 linux-libc-dev:amd64 poppler-utils:amd64 python-jwt:all python-libxml2:amd64 python3-jwt:all qemu-user-static:amd64 texlive-base:all texlive-fonts-recommended:all texlive-latex-base:all texlive-latex-recommended:all texlive-generic-recommended:all thunderbird:amd64 thunderbird-locale-en:amd64 thunderbird-gnome-support:amd64 thunderbird-locale-en-gb:all thunderbird-locale-en-us:all wpasupplicant:amd64 xserver-common:all xserver-xorg-core:amd64 xul-ext-ubufox:all liblouis-data:all liblouis9:amd64 python3-louis:all 
/usr/bin/dpkg --status-fd 17 --configure --pending 

And yes, unattended-upgrades are enabled in the configuration:

10periodic :

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Download-Upgradeable-Packages "0";
APT::Periodic::AutocleanInterval "0";

20auto-upgrades :

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";

So why is unattended-upgrades not installing any upgrades?

Requested extras:

ls -l /var/lib/apt/periodic:

-rw-r--r-- 1 root root 0 Nov 16 18:49 download-upgradeable-stamp
-rw-r--r-- 1 root root 0 Nov 17 12:50 unattended-upgrades-stamp
-rw-r--r-- 1 root root 0 Nov 16 18:47 update-stamp
-rw-r--r-- 1 root root 0 Nov 17 12:19 update-success-stamp
-rw-r--r-- 1 root root 0 Oct  3 11:18 upgrade-stamp

This is the entireity of /var/log/unattended-upgrades-dpkg.log:

Log started: 2017-11-17  12:10:41
Log ended: 2017-11-17  12:10:42

Log started: 2017-11-17  12:25:57
Log ended: 2017-11-17  12:25:58

Log started: 2017-11-17  12:50:53
Log ended: 2017-11-17  12:50:54

All three of those entries are from me running "sudo unattended-upgrades --dry-run" manually.

The previous unattended-upgrades-dpkg.log.1.gz contains this:

Log started: 2017-10-03  11:18:26
^MExtract templates from packages: 36%^MExtract templates from packages: 72%^MExtract templates from packages: 100%
Preconfiguring packages ...
dpkg: error: dpkg status database is locked by another process
Log ended: 2017-10-03  11:18:27

Note that this computer gets rebooted every day. Previous log unattended-upgrades-dpkg.log.2.gz is quite long and actually shows stuff being installed. It ends with this:

Found linux image: /boot/vmlinuz-3.11.0-23-generic
Found initrd image: /boot/initrd.img-3.11.0-23-generic
Adding boot menu entry for EFI firmware configuration
done
Setting up linux-signed-image-generic (4.4.0.92.97) ...
Setting up linux-signed-generic (4.4.0.92.97) ...
Setting up linux-libc-dev:amd64 (4.4.0-92.115) ...
Setting up xul-ext-ubufox (3.4-0ubuntu0.16.04.1) ...
Processing triggers for libc-bin (2.23-0ubuntu9) ...
Log ended: 2017-08-21  10:29:14