All doors have to lock within a certain amount of time if they don't then they unlock again.
If you've got a crook actuator it could be taking more time than it is supposed to or the BEM is not recieving the lock signal in time.
With the drivers window down, try helping the snipper button down into the lock position within the same time frame that all the other actuactors are working.
If it locks then you've most likely found the crook acutuator.

what about when they lock by themselves later (like few minutues-hour?)??