I've had it happen on a different esc. It's possible that a piece of dirt/grit got stuck there. Un mount your esc, unscrew the 4 tiny screws at the bottom of the esc and remove the bottom plate. CAREFULLY try and push the circuit board downwards by pressing on the heatsink. Or wiggle the circuit board about. The idea being if you gently dislodge the board from its mountings, the dirt should fall out.
The other thing is that the switch got dislodged. Locate the switch back in its proper position, reassemble everything and see what happens.