Another confirmed data point, with package delta and the specific malformed field.
Host: XCP-ng 8.3.0, xapi 26.1 (build 26.1.4), Xen 4.17.6-9.
Setup: XO from sources (community). All VDIs vanished from the per-VM Disks tab (XO 5 and XO 6); xe and the SR Disks tab show them fine; VMs run normally. Trigger was the 8.3 host update + reboot this morning — XO build unchanged since May 28, disks visible yesterday.
Host update delta (today): all 26.1.3-1.10 → 26.1.4-3.1 (xapi-core, xenopsd, sm-cli, sm-fairlock, xapi-storage-script, vhd-tool, message-switch, etc.), plus sm 3.2.12-17.8 → 17.9 as an independent bump.
The malformed field. An affected live OS disk (VM running):
is-a-snapshot: false
snapshot-of: <populated, points to another VDI>
snapshot-time: <populated>
A normal base VDI should have an empty snapshot-of. After the update, snapshot-of/snapshot-time are populated on real, non-snapshot base VDIs, and XO filters anything with a non-empty snapshot-of out of the per-VM Disks view — which is the disappearance.
The VDI that snapshot-of points to is a legitimate base image in my environment (a heavily-reused Win2022 build template with a large genuine snapshot/clone lineage), so I can't tell from the host side whether the parentage links themselves changed or only the snapshot-of on live VDI labeling did. Either way, the consumer-visible effect is the same.
REST confirms: /rest/v0/vms/<uuid>/vdis → []; /rest/v0/vdis/<uuid> → "no such VDI" for the VBD's referenced UUID, while xe vdi-list shows it.
Caution for others: since live disks now carry snapshot-like metadata, be careful with Health-dashboard "orphan" cleanup and snapshot deletion on affected VMs until this is understood.
Workaround that restored the per-VM Disks view: snapshot → revert → delete-snapshot (tested on a powered-off VM, immediate).
Happy to provide more diagnostics.