Ubuntu 18.10 - Issue with screen inactivity and lock screen

Same here after upgrading from 18.04 to 18.10. First tried to disable my extensions. After about an hour working I tried to lock my machine and failed. So not a solution for me.

Googling some more, when I came across Lock screen curtain in Ubuntu 18.10 won't open and a suggestion there was to remove and add gdm3 from terminal:

$ sudo apt remove gdm3
$ sudo apt install gdm3 
$ reboot

Now, half a day working later, 10+ locks, the issue has not returned.

Update 2018-11-16

Issues have returned unfortunately. After going through the bugreport this suggestion came by:

gsettings set org.gnome.shell.extensions.dash-to-dock transparency-mode FIXED

For me this seems to work.