Scottie is the rightest. The actuator wears over a jillion cycles, and the lock everything switch in the actuator that is supposed to trip all of the lock acutators is tripped at actuator rest position. It starts with exactly the behavior you describe, and ends up with the lock actuator in constant lock and even with the key, it is very difficult to unlock as you are fighting the actuator solenoid force. A temp "fix" until you can get at it is to pull the fuse for the pdl.

Not responsible for advice not taken...