Old post I know, however this may help someone out in the future. My avant does this every couple of years, one of the doors will play up and not unlock with the fob, lean through and pull the internal handle and then it’ll open from the exterior handle. Turns out that the lock/unlock motors in the locking mechanism get carboned up and stop working. Strip them down, clean the motor armatures with some meths and a scotch pad and they work for another couple years. Pics attached.