I do not know if this error message is related to your issue. Please attach the full log file(s) to make sure that we do not miss anything relevant.
Regardless of that, I would suggest to test with another greeter: - install unity-greeter (sudo apt install --no-install-recommends unity-greeter) - move or rename the file /usr/share/lightdm/lightdm.conf.d/60-lightdm-gtk-greeter.conf - reboot or restart lightdm Furthermore, you could boot into the live session of the Xubuntu 18.10 development release, and check if the problem is still present. Note that light-locker needs to be manually started. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1796374 Title: locking session turns off external monitor To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/light-locker/+bug/1796374/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs