Glad I was help to help![deleted]
What an adventure indeed! Just wanted to say thank you for saving me from a reinstall (although I was able to reboot using the Rescue Boot and had backups so it wouldn't have been a huge deal). I also didn't see any warnings of note during pve8to9 -full, and yet this caused a fatal flaw in the upgrade. My previous install was a vanilla PVE 8.4 install from ISO, so I'm not quite sure what went awry.
Ah well, all good now!