You could have an issue with an inner cable being pinched/broken in the base. I recommend dismantle and look inside. There is a small spot where the cable comes through to the ball. Or . . . .possibly a disconnect in there. The X/Y axis in analogue so it is strange why digital keys are being pressed.
Also, check if the stick has no issues where it mounts to the base. Remove and reset.
That's all I can think of.