The July updates batch that went out on 28 July carries xapi-26.1.11-1.3.xcpng8.3, and @kagbasi-wgsdac has since confirmed on https://github.com/xcp-ng/xcp/issues/825 that three days after patching his disks are all visible again and reverting a snapshot no longer duplicates VDIs.
The blog entry for that batch names the fix as non-snapshotted VBDs staying attached after VM.revert, a regression from xapi-26.1.4-3.3: https://xcp-ng.org/blog/2026/07/28/july-2026-updates-1-for-xcp-ng-8-3-lts/. Host reboots are needed. That stops new damage, but it does not unstamp VDIs that were already hit, so if disks are still hidden after you patch you probably still want the repair script at https://xcp-ng.org/forum/post/105564.
My post above also had the mechanism wrong, and @kagbasi-wgsdac corrected it: the field being wrongly written is snapshot-of on base disks, not is-a-snapshot.
If anyone is still watching disks disappear on a fully updated pool, please say so here, because that would be something new rather than the tail of this one.
