The problem is 2-fold, firstly by design in that we are using the Surface and not the Pro. This is a mobile phone processor and clearly not up to the job required.
Secondly is the VPN internet connection (at EK's insistence) that slows everything right down unless you are connected to a corporate network in which case it isn't then required.
The tablet tries to cycle, then because it's slow and the update doesn't work, crashes and can't be recovered.