There's something I wasn't able to search for and I'd like to ask the more experienced people...

Yesterday I noticed there was a group of enemies (I think Ironheads) that moved from one area to another, I sneaked around them as I went from Rail Crossing to the South protectorate base... whatever it's called... somewhat in the middle walking on the train tracks
When I went back, they weren't there anymore, but instead, they were just in front of Rail Crossing
It's like they moved over the train tracks
Is this a thing or was it some kind of a bug?

In addition, when I first came to Rail Crossing, I remember just to the north of the metro, before I went to sleep, I was curious so I quickly sneaked through some areas without saving the game, and there was a hole I could jump in
So I jumped in and ended up in some creepy cave, I decided to explore it the next day and quit the game
I haven't been able to find this hole since...
Is it possible that it disappeared?
I could swear it was just one/two zones far from the train... I found another hole but it's not the same one (I remember the previous one when I jumped down, I ended up among some corpses or skeletons and it looked really creepy, like a trap, whereas the new one I found it's just some psi beetles with psi related loot)