I am a fool.

So, I saw that players were encountering crashed UFOs, and the interior would spawn in such a way that the entrance would lead directly to a dead end. I checked and double checked the code several times over many months. I could not quite figure out what was going on.

Then I woke up this afternoon (after a nap) and thought I would check again.

There was nothing wrong with the code! The code was perfect!

It was the models. The different interior UFO tiles were named incorrectly, and some that should have had a western passage (leading to the exit) actually faced east, and blocked off the west side. So I've just renamed the proper files and all your UFOs should be fully explorable now!