I’m not sure if I can deliberately reproduce this one, but I’ve had it happen 3-4 times during this game.
In short, enemies will spawn right next to, or even inside, of my constructed buildings. And I don’t mean that they will spawn nearby and walk inside, I mean they spawn literally inside a building which has finished construction. At the same time, I get camps and other mobs spawning where they’re supposed to, so this seems to be randomly occurring. Furthermore, I’m not (to my knowledge) compressing or restricting the spawn areas in any strange way. I’ve had a hell of a time getting this single building constructed, but have some other farms and such nearby out of shot.
Have some screens:
I’ve had a couple of these camps spawn right here, they seem to really like this location. This one was while the building was in progress, but the second time they had spawned there.