Hi @simonp.
The problem is gone with commit 44e5b!!!
Up-to-date XCP-NG host and XenOrchestra VM were restarted after updating XenOrchestra.
I just initiated a full backup and all VMs - including my problematic machine - were backed up successfully without error.
Awesome! I will wait with closing until the scheduled delta backup is completed successfully, too.
Edit:
Scheduled backup ran without issue. The problem seems to have been resolved!
Thanks for all your work and assistance
Regards,
Marc