I think this Debian-reported bug is closely related. The description certainly sounds very like what I've experienced so far. I'm not linking it to this bug report until any relationship is clearer.
"policykit-1: please treat background processes (user bus) as part of active GUI session" https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=779988 ** Bug watch added: Debian Bug tracker #779988 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=779988 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1784964 Title: Regression due to CVE-2018-1116 (processes not inheriting user's groups ) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/policykit-1/+bug/1784964/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
