I found this passenger showing pathing errors and checked her details, it turns out she’s at the gate for a flight that’s only just come up on my Flight Monitor. I thought maybe she was there because she missed the previous day’s flight but the date is today’s. She’s not the only one, there are a bunch of them in this crowd for the same flight.
That’s weird. Can you drop your savegame to the Steam Workshop and post a link here? I am interested to check that.
Sadly I’ve played past this issue now and it no longer seems to happen but I may have found out why it was happening. I had an emergency flight where the passengers were left unboarded, and they couldn’t leave departures, so I fixed this by adding some stairs to the arrivals section below where they could go through customs and the security exit. Thing is, I don’t remember having an emergency issue with the flight in the screenshots above, but I played past the point where I could go back and check, sorry.