Something in the shutdown triggers a start of a service or doesn't stop in time. Since something is still running the shutdown never completes.

Looking at the screenshot for instance it says "Stopping monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling...".
But there is no acknowledgment [OK] that it has completed.

I'd start looking there.

Pretty sure you just have to pop it in the microwave for about 60 seconds... full power... should get it all sorted.

Looks like

xm shutdown -a

will shutdown all of the vms