I think I found a workaround. I noticed the traceback I saw in syslog happened a lot before I tried to log back in and I deduced it happened when notification were displayed on my locked screen.
Since I disabled notifications on my lock screen (Notifications > Notifications on lock screen) I haven't encountered the bug anymore. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1685141 Title: System freezes after locking screen To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-screensaver/+bug/1685141/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
