If a mount uses the hard mount option, it will lock any process touching it, including unmount during shutdown, if the mount source is unavailable. It is a kernel thing and I believe there is no solution for it at present.

@hrvojer I can't tell for sure without detailed troubleshooting, but your crash reminds me of a bug in XenVbd that was fixed in the XCP-ng 9.1.200 tools (Apr 2026). It's unlikely that updating to an old Xen tools version would help in that case.