I use Mate as my desktop environment and I recently upgraded from 16.04 to 18.04.
Since the upgrade, I now have two lock screens. If I lock my screen (Ctrl-Alt-L), I get the expected Mate screensaver, but sometimes when I unlock it I get an additional light blue lock screen, just containing a password field.
I end up having to unlock both to get back to my desktop. The last time this happened, the blue screen didn't show a password field and I had to reboot my machine.
I think the blue lock screen is being fired from a timer, somewhere. If I leave my computer locked for long enough, the blue screen will be waiting for me. However if I briefly lock and unlock my machine, only the Mate screensaver appears.
Any ideas what this is? After researching some similar issues, I tried removing
gnome-screensaver, but it hasn't fixed anything.
This question is related, however I upgraded rather than a fresh install. Also I have two lock screens, not three, and I've already removed gnome-screensaver.