if the plunger is sticking in the coil after you turn the power off, the problem is almost always mechanical and usually gunk or wear in the coil sleeve is wedging the plunger.

also look for a mushroomed plunger - check if it has a sharp ridge around the end and make sure the coil stop is ok. If the coil sleeve is metal, see if it's distorted on the end opposite the coil stop.

the difference between you pulling in the plunger and the coil doing it is the coil does it a lot harder.

if nothing obvious, you could try swapping pieces with another reel and see when the problem moves.