Update - Overdue.
Moved the car to a family member's house, it was on the bump stops and ouch, bumpier than I remember the last time. Glad it was only 10 miles.
With credit to the guys who had it, they are really good specialists, and I think they gave up as it was costing them a lot of money in time. Checking over everything there is nothing obvious that they have done to cause this, possibly a coincidence.
They did find corroded connections behind the passenger kick panel and repaired some of them that required repairing. Comms to the BECM is fine, all seems to be working from my Hawkeye Total. 1 error was reported to the passenger seat outstation/module (I will worry about that later, it's been there for years).
The current situation is:
Start the engine and the compressor runs for 10 seconds maybe, then powers off giving an EAS fault and 35MPH Max on the display.
EAS lights all flash from then, and then they go solid.
The compressor is a brand-new Dunlop.
I did not have time to hook up the laptop and run EAS unlock, that is the plan for this weekend along with checking the continuity of the pressure switch (no longer need to do the thermal switch as it's new).
Will have the emergency inflation valves then too, so I can pump it up leave it and see if it loses any pressure.