I think a voltage spike can cause it, maybe from the throttle hall sensor. If the controller reads a high voltage reading it will go into protect. Try picking up the motor wheel off the ground and then opening the throttle without load and see if it powers up. Also, as you say just switch off and on again and this can sort it. However, i have seen this on my maxe and on a friends and both eventually went dead without warning when charging.
Also check low and high voltage cut off values, although if the bike was working previously ok, then unlikely these are the cause.