Aerospace safety investigations on accidents and in this case an incident ... are about finding out what happened, then why it happened, followed by devising and implementing ways to prevent it from occurring again. They are neither about clearing nor blaming anyone.
At this stage it still is about ...'What'... Which means, like @DaveReidUK posted, listing possible scenarios. Hope for better and more detailed pictures as well as more information.
@ErwinS... Would be interesting if you could provide public domain links to similar cases (you suggested there are some) or Boeing bulletins.