I found the problem!
After making sure the power settings were correct, I unplugged and reconnected each of the USB cables and video connectors (they make the same bingeley-bong) but it made no difference.
I made sure that each usb cable was connected to a port or powered hub easily able to supply the power. I removed unneeded USB devices
Still random usb disconnects/reconnects even when nothing is running, noone is near the pc.
Then I noticed that the settings jog dial of one of the touchscreen monitors wasn’t looking right.
Took the back off the monitor to discover that the electronics are all on a small circuit board, which was glued, not screwed, into place.
The glue simply wasn’t sticky any more, so the circuit board had moved inside the case. When I plugged usb or hdmi plugs in, they weren’t going all the way into the sockets, making an intermittent connection.
Five minutes later, my hot melt glue gun (branded Woolworths, so not entirely new) had fixed the problem.
All is now good, it was not the fault of Asobo, not the fault of Microsoft.