Thanks for the versions.
If I read the changelogs right, sm-3.2.12-25.2 is one build after the 25.1 that @dthenot mentioned and still carries its QCOW2 patches, and the release note for blktap-3.55.5-12.3 says it fixed a tapdisk crash during backups (https://xcp-ng.org/forum/post/109336).
So unless I missed one, you already have every fix I know about.
I think this might be a different bug. I can't tell from here why tap-ctl close times out on those snapshot disks, so that one is for @Team-Storage.
I'd guess the SMlog from both hosts around one failed run is the first thing they'll ask for.