My headphones are actually the Marshall '''Monitor''' Bluetooths, rather than the '''MIDs''', but since there’s no Monitors in the list and the power button is the same design (at least from the outside) the solution is likely the same.
The power button doesn’t work. It stopped working when the headphones were unfolded but would work when the headphones were folded up. Now nothing. Often when moving the headphones around with the button pressed, the indicator LED would flash super fast, like it was shorting, but the headphones now don’t turn on.