The most common 18.10 stack trace I've seen people report is due to the transparency setting. However anything that triggers an exception in Dash to Dock when it is disabled on the lockscreen produces this issue so there are many possible causes.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/237 -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to mutter in Ubuntu. https://bugs.launchpad.net/bugs/1799430 Title: Icon dock visible on lock screen Status in gnome-shell-extension-dashtodock package in Ubuntu: Confirmed Status in mutter package in Ubuntu: Confirmed Bug description: When locking the machine with alt-L the icon dock is still visible. After Login, the dock does not get adjusted to the top menu. In rare cases, the dock does not respond any more. This requires a reboot of the machine ProblemType: Bug DistroRelease: Ubuntu 18.10 Package: mutter 3.30.1-1 ProcVersionSignature: Ubuntu 4.18.0-10.11-generic 4.18.12 Uname: Linux 4.18.0-10-generic x86_64 ApportVersion: 2.20.10-0ubuntu13 Architecture: amd64 CurrentDesktop: ubuntu:GNOME Date: Tue Oct 23 12:59:27 2018 InstallationDate: Installed on 2018-04-30 (176 days ago) InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426) SourcePackage: mutter UpgradeStatus: Upgraded to cosmic on 2018-10-20 (2 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell-extension-dashtodock/+bug/1799430/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
