As an ex -400 driver I have fought my way through a lot of the 504 posts.
Of these, about 30 contain INFORMED comments about the 400. The rest should keep there comments to something they know about, like their own type, if they have one! ( ie- there doesn't appear to be a cargo door there!).
I wouldn't be at all surprised that there will be an accident report that will tell us the facts.
Happy flying.( to those that do!)