Comment 4 for bug 1852903

systemd crashed while trying to serialize, on a service that appears to not be provided by Ubuntu, '/lib/systemd/system/keepsessions.service'. It looks like it's part of a 'sitetools' package (the exec command is "/opt/sitetools/keepsessions").

This is probably a bug in systemd, but it would help to see the specific details of that service file; can you attach or paste it here?