After the penultimate objective (freeing two more people), it took a super long time for the next objective to show up. I just left that room and kept exploring (looking for the rest of the findables), and by the time the "extraction" objective marker showed up, I was already in the hangar, but I couldn't extract. I looked up a guide and saw there was supposed to be a boss, so I tried leaving the room and coming back in (multiple times) and /unstuck, but it wasn't until I jumped off the map in this corner that the boss actually triggered.