Surface Pro 4 keyboard stopped working

[jmak]

As per title. We have a number of these. They're all 3 years old and on the same build but the keyboard (official type-cover) on one no longer responds either to keyboard or track pad input and there are no backlights either.

 

Things I've tried:

 

Cleaning the contacts

Swapping keyboards with another device

Re-imaging with the base image that all of the others use (running Windows 1803 education)

 

USB keyboard and mouse work. All MS Surface drivers installed.

 

TIA