I have to wonder if the loose bolts are an additional problem not really related to the door falling off. Bolts should have lock wire keeping them in place. Even if they are loose, a door could be rattling or hissing air, but I'm not sure how it comes off.
I'm not an ME, or a manufacturer, so I could be wrong, but if so, I'd like to know how that happens.
A current working theory (from people more expert than me) is that Spirit Aerosystems (who builds the fuselage) does a loose install of the door for transport to Boeing, who then does a final install of the interior. Since this door is usually removed for the interior installation the theory is that it isn't and the loose install is what has ended up on otherwise flight worthy planes.
Always seems weird to me, like they aren't going to be making plans bodies for many other customers, so now Boeing has to pay extra for each body since now spirit aerosystems wants to have growing profits on every thing they make.
I was recently in Wichita at the airport where spirit aerosystems builds fuselages and could see a large Boeing plane that transports the fuselage inside it to Washington to be finished
This principle is named after a rock band (Van Halen), who had a “brown M&M’s clause” in their contracts with event organizers, stipulating that the organizers must provide M&M’s in the backstage area, but that there must be no brown M&M’s available. This small clause gave the band an easy way to check whether organizers actually paid attention to all the details in the contract, which was important given how complicated and potentially dangerous the band’s production was.
The fuselage is manufactured in Kansas before being shipped by rail to Washington for final fit-out and assembly. The door plugs are put in place in Kansas, but not tightened down to flight spec because it’s expected that Boeing will take them off again to fit out the interior, then bolt them down to spec. One theory I’ve heard is that Boeing’s not using the plug doors to move in seats and lavatories and what have you, and no one thought to double check the plug doors afterwards in Washington because no one has touched them since it arrived from Kansas.
I'm not any of those things either, but I do subscribe to Mentour Pilot on YouTube who mentioned that there had been previous flights of that plane with cabin pressure issues.