I just had the same issue pop up last night. After isolating the problem to only the push buttons on the top of the joystick, I disassembled the hand grip. The result was 2 of the colored wires that come up from base had snapped off of the wiring board within the handle. I probably could have spliced in new pieces of wire to reconnect them but decided it was better to buy a new HOTAS all together (mine has only seen light usage for 14 months).
It is unfortunate because the throttle works perfectly.