I have a feeling it was related to running out of disk space during the upgrade, since I upgraded to 18.104.22.168 this time and it warned me there wasn't enough free space. After deleting a few backups it installed fine.
And yep, configuration evaluation means I might be able to give up the Java client entirely! I also noticed some extra end-system events related to authentication which is nice.
Well, the upgrade was an abject failure, after reboot it had no network and I couldn't even log in as root on the console or get grub up to boot single user. At least I had the presence of mind to take a snapshot beforehand.