Q: Driver's door locking intermittently

The driver's door sometimes locks intermittently. While sitting in the car, I can push the button all the way down, and someone outside can sometimes still open the door. If I use the key, it doesn't always lock the door, even though it has worked in the past. The lock button will not go fully to the top. Sometimes I can lock the door and go out the passenger's side door and it will still be unlocked.