Usually worn parts causes this. If you can adjust the coil stop so the bar doesn't reset too high that helps (I don't think Bally has this seems like Gottlieb was the only maker that did).
Check for play in the fiberboard link on the plunger. If it resets too high and you check the fingers that go through to the back plate and they go off the track or too high - due to flexing of that plate it won't be as flush as it could be - bend back a little to compensate. Check for play in the fingers. Check for excessive wear on the coil stop/plunger.
