I am seeing this exact same problem. Performed a fresh install of 18.04 LTS and have remained updated the whole time. Still seeing problems with gnome-shell filling the logs. This seems to happen when the user session in gnome goes to the lock screen and you can see it go black momentarily, then recover.
Log examples: Sep 18 14:29:08 machine org.gnome.Shell.desktop[2266]: #5 0x7fff48999630 I resource:///org/gnome/gjs/modules/_legacy.js:82 (0x7f48b80b5de0 @ 71) Sep 18 14:29:08 machine org.gnome.Shell.desktop[2266]: #6 0x7fff489996f0 b self-hosted:916 (0x7f48b80f12b8 @ 367) Sep 18 14:29:08 machine gnome-shell[2266]: Object St.BoxLayout (0x5587958dee60), has been already finalized. Impossible to set any property to it. Sep 18 14:29:08 machine gnome-shell[2266]: Object St.Icon (0x558793ecab90), has been already finalized. Impossible to set any property to it. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1792702 Title: gnome-shell filling /var/log/syslog with "Object St.Icon|BoxLayout (...), has been already finalized. Impossible to set any property to it." To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1792702/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs