😮💨 New backup passed the integrity checks.
Discussion
Got the old drive out of the enclosure and my other enclosure acts like there's no drive there. I can feel the disk spin up, but it doesn't even attempt to register anything on the computer side. Could be a 4TB limit thing. The 3.5" drive I took out was 3TB.
The closest configuration I have to working with the old drive is in the old enclosure and it doesn't see a partition table, fdisk tells me /dev/xvdi isn't there (ls disagrees), and Qubes can't parse the partition table.