And the next paragraph:

The jet had been prevented from making long-haul flights over water so that the plane "could return very quickly to an airport" in the event the warnings happened again, NTSB chief Jennifer Homendy said.

~~Which makes it sound like they couldn't find the source of that warning but weren't willing to completely write it off.~~

Nevermind:

"An additional maintenance look" was requested but "not completed" before the incident, Ms Homendy said.

Apparently it started immediately after Alaska installed their wifi equipment, which some sources have indicated requires opening that door plug. They apparently assumed it was due to the wifi install. Should have grounded it until the figured it out.

Alaska does have a history of poor maintenance causing crashes.

Ex-aircraft mechanic here. Nothing will have been done in this situation without paperwork backing the decision. There are often small niggles that could ground an aircraft, but there are manuals that can be consulted to see how many more flights can be taken before it must be grounded for rectification - the MEL (minimum equipment list) and CDL (configuration deviation list). So the airline will not have made the ultimate decision to keep flying, Boeing will.

The fact that this has now been found in two different airlines means that it’s a design flaw again, either the locking mechanism on the bolts is insufficient, or the reinstallation instructions in the maintenance manual is incorrect (the Alaska airlines aircraft door plug was recently removed to carry out maintenance on another part)

Agreed. This is a multi-layered fuckup. The manufacturer probably didn't tighten things down all the way, their QA didn't catch the critical defect, the plane inspectors didn't catch it during inspection, the airline didn't ground it after a pressurization warning, the pilot flew a plane with a known issue. There are several cultures of complacency at play. Hopefully the FAA can scare everyone into flying right.

Failure is a chain.

More like unexpected new features, like the all new spontaneous exit row!

I wonder how many cents they saved by not ensuring the bolts were properly tightened.

I don’t get why they don’t just make it a bit bigger on the inside so that when pressurized, the pressure itself seals it. Seems like a fail safe solution instead of this shadiness.

It’s a door plug, which means it’s meant to be replaced with an actual door if required, so a lot of the hardware for an actual door are in place. Doors are designed to slide in, then raise up so the stop pins engage the stop fittings from the inside, so the door is in effect bigger than the hole it’s in. this video provides a detailed explanation of how it works.

The big issue here is that the airplane is only 2 months old, it was delivered from Boeing in late October. Which means it’s either a design flaw or a process flaw in the original manufacturing. This smacks of corporate cost cutting again. Boeing are totally on the hook for this and it’s only lucky there were no lives lost. You watch, they’ll blame it on the airline initially but the fault will come back round to them again.

That's how the normal doors work because they aren't permanently secured in place. The reason is weight as it pretty much always is in aviation design.

“Oopsie-daisy!”

— Unities Airlines

There's a one-sentence quote here, what do you expect them to say exactly as they find things wrong?

Better you're on the airline where they found the problems than the airline that didn't.

Ah, playin' it safe, are ya? Why not spice things up a bit? Flyin' United, might as well throw in a bit of turbulence for the craic!

Here is an alternative Piped link(s):

front doesn't fall off

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Well, as long as it's not in the environment, at least.