I have ubuntu 16.04; the login screen behaves inconsistently. Sometimes when I open my laptop which had been suspended, it goes to the login screen, but the box to enter my password is missing. Sometimes the toolbar is also missing. Possibly related, when I open from suspension sometimes I go to the login screen, but sometimes it just returns me directly to my desktop without logging in, which is a security risk.
I have been having this problem since I installed last month, but rebooting fixes it. I would like to resolve the underlying issue though.
Are you using lightdm or gdm3 as your login screen? You can try
or