I have a fleet of vehicles (Hyundai, Mercedes, Toyota, Volkswagen, Honda) all which have a GPS tracking device attached to their OBD2 port. Of this fleet, a subset of the vehicles are Mercedes-Benz Vitos W639's manufactured in different years.
Whenever the GPS device is attached to their OBD2 port, the central locking often will stop working. For some of the vehicles it only happens very occasionally. For some of the vehicles, the central locking rarely works. This usually requires that the van needs to be opened manually. However, once the van's engine has started, the central locking usually starts working again. For whatever reason, this issue seems to be very specific to the W639. I also have Mercedes sprinters and this never happens nor does it happen to any of the other vehicles.
Often when the central locking is not working, I will remove the GPS from the OBD2 port and it instantly starts working again. Soon as I plug the GPS back in, it stops working. Obviously, I need to have this GPS installed for tracking otherwise I would just remove it.