Unfortunately, it seemed to hang at some stage during the shutdown process. I could still ping it and run some WMI stuff but I couldn’t rdp back onto it.
On a virtual server I’d have powered it off an back on again, but obviously that wasn’t an option, and I don’t have server room access.
This relatively significant – it was a production server and I was in danger of not being able to get it back up.
Anyway the fix was to use the PowerShell restart-computer with -force, as follows
restart-computer -computername server33 -force