Assuming the door is fully installed but deactivated and the aircraft hasn’t been through a heavy mx check then it looks like a Quality issue from build. It would be interesting know if any reports previously of door indication / noise/ pressurisation problems. Maybe even a certification issue with the length of the fuselage flexing on landing. Going to be an interesting investigation with as always a lot of Swiss cheese hazards leading to the event. Luckily the seat was empty as could have been far worse.