It took me a while to pin this one down, but I've been experiencing a bug with Duplicant pathing through Mechanized Airlocks without valid permissions. I did find this old issue, but in my case the access is clearly left-to-right only, with no top-to-bottom access available.
The setup pictured here is designed to permit door access for only a single designated astronaut, for when it is time to board a rocket. Other duplicants can access either side of the door; the left side should have Atmo Suit access only, with the right side only having Jet Suit access. No astronauts are allowed access to Jet Suits - I don't want my dupes absconding with them on long rocket trips.
- The Mechanized Airlock prohibits all access for all dupes but one - the designated astronaut.
- Despite this, I've seen dupes cross the door in both directions.
Check out Nikola below - his access permissions for the airlock are disabled.
Despite that, he's got a planned pathway to an errand on the other side, violating those permissions.
The attached game-save was made at this exact frame, still paused. I've only caught Dupes in the act two or three times.
That said, I've had it occur many more times without me witnessing it; I know when it happens when Jet Suits start showing up in nonsensical locations within my base. The base's setup is such that Jet Suits should only ever show up in the Space biome. (Note that this doesn't currently hold true within the save, as I still have to hunt down one more stray suit-wearing Dupe from a previous breach, not including Nikola here.)
If you'd like to repro this, I don't have a perfect setup, but the attached game save tends to see this happen from time to time whenever Dupes have activity in the area of that dual rocket silo.
I'd advise making a few dig errands on the left-hand side (Jet Suit accessible only) and watching how Dupes path their return from those dig commands. Either the regolith pile-up against the left-hand wall/Neutronium or any regolith buildup above Bunker Tiles in the area should suffice.
Here are a few details that probably aren't important... but I know from experience (as a software developer) that there's a chance these details are. Please note that I have not thoroughly tested (as if I were "on the clock" at a job) to determine relevance.
- I've only ever seen them do it whenever the Gantry's extended.
- Because of that previous point, I've only seen it occur for the airlock on the right-hand side. (The rocket to the left only recently returned, and I generally keep gantries retracted while the rocket's away. I have no way to know which airlock of the pair is used if I don't directly witness it.)