How to unlock a stale Proxmox qemu VM?

I have a stale Proxmox (qemu) VM.

I have tried qemu unlock ... and I tried to delete the lockfile (permission denied).

Is there any other way as rebooting the hypervisor to release the lock?

Clarification:

I try to reboot a VM, but the shutdown hangs (since hours), than I decided to halt it, but that fails because of the lock. I have tried to remove the lock as written above