My 2010 XF S has this problem. Intermittently. With the O/S rear passenger door.
I unlock the car in the morning and drive to work. Upon arrival, the car will not lock. I need to open the rear passenger door from the inside, then close the door, and the locking system works.
This tells me obviously that he rear lock is not unlocking with the rest of the doors. Can this be rectified or will I need a new lock?
To be honest, if its going to be pricey, I may as well continue to reach to the back door and open it whenever I get out of the car as opposed to £100s in repair costs.