How to fix Ubuntu 18.04LTS freezes?

I've installed latest Ubuntu 18.04.1 LTS about a week ago.
All the soft was installed via system menu or Jetbrains repo.

In 2 days appeared freezes - only mouse moves, irresponsive to keyboard, timer above the window don't tick. For several days it was 1 freeze a day in the evening, then 2 freezes in the evening, yesterday 5 freezes, today - 5 times.

I daily do update/upgrade.

My keyboard don't have SysReq button.

Ctrl+Alt+F2/F3 worked only once, once Ctrl+Alt+ScrollLock added somewhat in appeared console stream.

I googled around and find this post advising to get to /etc/default/grub and changing the default line to GRUB_CMDLINE_LINUX_DEFAULT="noacpi" and then running sudo update-grub.

Then i had my 5 freezes yesterday. Sometimes after crash Ubuntu asks for sending crash report, sometimes not.

My questions are:

1. How to get to console and collect info/reason for a crash?
2. Is it possible to recover from crash without reset or power down button?
3. How to properly collect info/reason for a crash to send it to Ubuntu (preferably automatically)?

There is an advice to change kernel in this link.
The kernel in my setup is 4.15.0-39-generic. But it is not in a list of available stable kernels.

Should I change to another kernel in order to get stable system?

Update 2018-11-29

    /var/crash$ ls -alt /var/crash
total 25864
-rw-r-----  1 gdm       whoopsie 19808573 ноя 29 09:38 _usr_bin_gnome-shell.121.crash
drwxrwsrwt  2 root      whoopsie     4096 ноя 29 09:27 .
----------  1 gdm       whoopsie  1810565 ноя 28 15:16 _usr_bin_Xwayland.121.crash
-rw-------  1 whoopsie  whoopsie        0 ноя 28 14:07 _usr_bin_gnome-shell.121.uploaded
-rw-r--r--  1 root      whoopsie        0 ноя 28 14:04 _usr_bin_gnome-shell.121.upload
-rw-------  1 whoopsie  whoopsie        0 ноя 28 10:08 _usr_share_stacer_stacer.1000.uploaded
-rw-rw-r--  1 home-user whoopsie        0 ноя 28 10:05 _usr_share_stacer_stacer.1000.upload
-rw-r-----  1 home-user whoopsie  4845874 ноя 28 10:05 _usr_share_stacer_stacer.1000.crash
drwxr-xr-x 15 root      root         4096 ноя 20 20:09 ..

and

/var/crash$ sudo ls -al ~/.local/share/gnome-shell/extensions
[sudo] password for home-user: 
ls: cannot access '/home/home-user/.local/share/gnome-shell/extensions': No such file or directory

and

/var/crash$ free -h
              total        used        free      shared  buff/cache   available
Mem:            31G        3,1G         25G        118M        3,0G         27G
Swap:          2,0G          0B        2,0G

Yes, memtest does appear in my GRUB menu. I'll give it a try tonight. Dual-boot Windows 7 don't show any problems so far.

Just have found quite similar issue with LibreOffice 5.1 / Ubuntu 16.04:

Turned off Java in my LibreOffice, OpenCL already off. No luck. 3 freezes in 2 hours. Last time touching LibreOffice after a pause freeze everything but mouse again. Installed NVidia driver v.340. Let' see.