You want to hear something funny? Recently this happened in mine. I found that the plastic locking button which screws onto the metal rod coming up through the door panel for some reason was providing just enough Resistance most likely due to the metal rod getting bent somehow that simply unscrewing it and removing it resolved this issue.. I have left it off till I can get the door panel off and restore the lock rod to a more accommodating orientation.
Something is providing some resistance in the locking system.. It may be a defective actuator.