Not PM owner but on Sprinter had problem with sliding door.
You might check sensor contacts on doors and make sure latch is well lubed. On my Sprinter to try fix before new latch came in the dealership "cleaned" latch. Never replaced latch because after cleaning and lubed lock behaved.
So, now when lube the wheelchair lift get hinges and door latches sprayed down with silicon spray lube.
I used to have this problem, took care of it myself because the dealership is worthless and I can't afford to be out of my van for 1/2 a day or more. The latch on the door frame (rear side) is held in place with 2 Torx head screws, because you have to slam the side door to get it shut the latch gets out of adjustment. Simply loosen screws and adjust until the door shuts fully AND you can still open every time.DO NOT over tighten screws, they will break off! There are small notches on the frame and the bracket. You can also adjust the latch on the door itself, also 2 Torx head screws. The latch for the rear doors is on the floor and also has 2 torx head screws. Good luck, it is a very fine adjustment and may take a few attempts.
I believe there are pictures posted in another section of this forum.