I had this (or very similar) with one system. They had a default server setup, but with the backup with DAR contrib as well. I updated the contrib manually, and then ran
signal-event post-upgrade; signal-event reboot
I'm not sure which of the two fixed it, but it then worked fine. I suspect it was running the above commands, but that is a gut feeling, rather than anything I can back up with evidence.
HTH.