As this is still an issue in 2020 - I might have found a solution for at least some cases (happened to me just yesterday/today at the end of an already loooong workday, when I had no more patience to wait any longer before starting my 2 hour ride home after midnight):
After about an hour of waiting and no reaction whatsoever i tried pinging all the VMs running on the stuck HyperV. Eventually one DID answer the ping (damn them Exchange-Servers...). I tried to shut the VM in question down forcefully with "shutdown /i" (CMD) which just resulted in a "permission denied" message (could have to do with the reason the HyperV had issues putting it to hypernation/pause).
I then tried to connect me to the server via RDP which worked like a charm. I manually shut the server down within it's own gui and just a few minutes later the HyperV was successfully rebooted. Only had to restart the trolling VM in HyperV and everything was alife and kickin' again.
May have been a fluke, still have to verify next time (or better shut down the VMs beforhand anyway...), but hey, I would have loved that straw yesterday...
All the best to all admins-pals out there,
Arno
