Unconfirmed reports that the newly-discovered door plug has one of the two guide rollers jammed in the guide. Given that they are part of the aircraft structure and not the door, if true it would imply that it had sheared off.
That would be an interesting failure mode. Given that the photos appear to show the aft roller still in situ in the doorframe, it would have to be the forward one. With no guide roller engaged in the door, the presence or absence of the locking bolt would be irrelevant and it may have allowed at least the forward edge of the door to creep past the stops.