FirbyKirby

Just to close the loop on this if anyone finds it in the future, I never solved this, but had good backups, so I took a risk and just removed the old cache, set up shares on the new pools, and restored from backup. That actually had similar problems, but they were in non-critical files that I was able to manually remove and delete, and successfully complete the restore.
 
FWIW, I think the mover might have been choking on my Kasm container. Kasm uses docker-in-docker and requires bypassing the FUSE FS. So, I think the files in question are related to the docker in docker containers of some of the workspaces I setup in Kasm. Certainly, when  I had issues restoring from backup, it was these container files that caused the issues. I ultimately deleted my Kasm appdata folder from the backup (it didn't have anything important in it since the config was stored in the template on the flash drive) and re-installed Kasm on the new drive without any loss of data or functionality.
 
So, all in all, it's "fixed" though I don't really understand why it failed in the first place, and the way I got back to normal operation does bother me a bit for the future.

I was able to solve this using the thread https://forums.unraid.net/topic/102194-priority-of-active-backup-bond/. Linking here so others may benefit.