It seems that large groups spontaneously expand behind lines and when assaulting bases. The usually spawn around you or another friendly unit. In late game you can easily find yourself instantly surrounded by 100 biters and insta-dying.

It tries it's best to avoid this issue by tracking group position and "lagging" spawn position by some ticks behind of squad's position. If you can provide savefile, then i can fix this in future.

Same problem. Biters decompress too close to players and player structures. Possible solution is to force biter decompression when they are within x chunks of a player or player structure.

Another problem exists with biters warping over water, i.e. escaping an island.