I have some memory of a report similar to this where biters would try to attack the player and when they got close they would all "bounce" away. Something about the tightly-packed logic of biters decides that it should "spread out" the packed biters and does it similar to this.
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The issue is that the “bounce” speed is given by how close they are together, so if they're really close, they'll get bumped really fast. I limited it to the normal unit speed, which fixes it in this particular case. I'm sure within 5 minutes someone will show up with a mod that changes biters max speed to the speed of light and say it happens again, and I'll move that one to Won't Fix.
I'm sure within 5 minutes someone will show up with a mod that changes biters max speed to the speed of light and say it happens again, and I'll move that one to Won't Fix.
This is good to see. I didn't think to report it before, but reading the OP reminded me I had seen similar behavior on a test map in map editor where I used cliffs to block off access to some stuff on 3 sides, forcing the biters to go around (effectively funneling them at the defenses I was testing), but occasionally I was seeing some bypass the cliffs (some groups were having trouble getting around the line of cliffs I had set up and so were massing up against the cliffs).
This may be the problem I was experiencing when a biter nest mysteriously appeared on the wrong side of a cliff once. I still think though, that this was the nest appearing on the other side of the cliff when the biter created it.