i wouldn't be surprised if there wasn't some kind of hardware security measure. like there has to be a resistance measured from one of the pins or shorting two of the pins to make a connection, that yes, there is voltage on this pin or this circuit is closed, so this is approved hardware and then can boot & be used. and as little documentation there is on these, it would be a guessing game at best.
you might have better luck tracing the matrix & just wiring the matrix straight to the pro-micro (totally bypassing the built in controller and whatever protocol it runs). cut traces as needed.