I should have taken a pic of my situation because it actually looked like the lab overwrote some of the ant hill, but in your case I don’t know where it went. Interesting.
Looking at the right side of the ant colony, however, I can make a guess. It looks as if it spawned at the edge of an overmap section. And there was not enough room to spawn the queen chamber, hence the dead ends. Does the top (surface) map have a sort of ‘line’ where forest/swamp/fields spawned? Like maybe located in the same place the dead ends are to support this?