I tried this on my lab (with XO 6.9.1), moving the pool master to the other host with xe pool-designate-new-master and then back. XO stayed connected both times and picked up the new master, even though Settings > Servers still showed the old host's address; on the way back it took a minute or two to catch up.
I didn't test 6.2.2, and I used the CLI rather than the XO 5 Advanced tab, so my guess that your older version is the difference is only a guess.
For the XVA, I'm not aware of release notes for the appliance image itself: it updates itself after import, and the notes that exist are per XO version, in the monthly blog post and the changelog, both linked from https://docs.xen-orchestra.com/getting-started/releases#release-cadence-and-channels .
How often the downloadable XVA gets rebuilt I don't know, so the 2025.12 tag may just be the date of the base image, but I'd rather ask than guess.
