United Airlines has been inspecting all it's 737 Max 9 aircraft plug doors (the part that went POOF! and disappeared on the plane this weekend), and found loose bolts on 5 , so far...

 https://theaircurrent.com/feed/dispatches/united-finds-loose-bolts-on-plug-doors-during-737-max-9-inspections/

Other possible defects were exposed during the explosive event. When the cabin depressurized, the cockpit door flew open, banging into a lavatory door. That door is supposed to be sealed to prevent external access by potential terrorists. Yet it was somehow unable to remain closed when the cabin lost pressure. It sounds as if that issue will require further attention as well.

https://dailytimewaster.blogspot.com/2024/01/in-follow-up-to-alaskan-airlines.html