Yes it is working in test screen.
It also reacts to power on button as soon, as a USB power source is plugged in.
Looks very much like some strange hardware defect, as the other two devices are working perfectly well.
I recently got three M5Paper.
Two are working perfectly well, but one has a huge problem. It won't switch on if on battery.
As soon as I connect USB I can activate it, and after unplugging USB it just runs fine on battery.
But as soon as I switch it off it cannot be reactivated again. No problems at all with the other two decives.
Already tried flashing newest firmware. No resolution.