My passenger front door would do exactly what you describe, and I assumed it was one of the back doors, for the same reasons you list (higher likely hood of bad connections in back). After more trouble shooting I decided it was the front lock actuator and ordered a replacement. Before installing the replacement I cleaned the gunked up latch. At that point I decided to see what would happen with my old lock actuator and it worked!svaric, are you saying the front doors will power unlock after pressing the lock button on the center console, or after manually pushing in the interior door handle?
The Sprinter's lock controls have this weird programming where if a lock command is issued by any means (center console button, key fob, or manual locking), it will check the status of each door lock, and if one of the doors remains unlocked, it will power unlock all doors. If you immediately re-lock manually, it will lock, unlock, and lock again. This can be triggered by one of the locks physically not moving into locked position, or the circuitry that senses the lock state isn't completing the circuit. It's commonly caused by weak contacts in the rear doors or sliding door. Note that these contacts are not the same switch that activates the dome lights.
If you're physically pushing one of the front door interior handles into the locked position to activate the power locks, and the power locks then immediately unlock all doors, my guess would be that the problem is in the sliding or rear doors, not the front doors.
So even though the back is a more likely candidate, it could still be a problem with the front.