@florent I updated XO to master 60ba5, and still having the issue.
I don't see any errors in the backup log. It just says "isFull": true for the ones stuck on full backups.
The XO log just reports:
Mar 24 16:26:47 xo1 xo-server[21199]: 2026-03-24T20:26:47.315Z xo:backups:worker INFO starting backup
Mar 24 16:26:52 xo1 xo-server[21199]: 2026-03-24T20:26:52.359Z xo:xapi:xapi-disks INFO export through vhd
Mar 24 16:26:54 xo1 xo-server[21199]: 2026-03-24T20:26:54.410Z xo:xapi:xapi-disks INFO export through vhd
Mar 24 16:29:22 xo1 xo-server[21199]: 2026-03-24T20:29:22.250Z xo:backups:worker INFO backup has ended
Note, it reports two export through vhd and does two full backups and one delta.