2000 Ford Expedition, 110000 miles. After-market alarm system.
Almost every time we unlock the doors, one doesn't unlock, sometimes two. It doesn't matter if we are unlocking with the remote fob, the door number pad, or inside with the unlock button. The one that won't unlock varies: most often the tailgate, then the two right-side doors, rarely the driver's door. Sometimes re-locking and unlocking will get it to open. We don't think it's an actuator, because isn't there one actuator per door, so a bad actuator would always affect the same door?