Can the spitters get in range of the turrets? I'm not sure how the pathing works, and it would be wrong for the biters, but if the spitters are able to attack the turrets, that could have something to do with it. Again, I don't really have any idea how this works, i'm just spouting off random ideas...

Do any of your mods affect aliens? I'd look in your mod folder, but (for various reasons) I can't at the moment. There is no mod modify aliens. I've checked every codes within mods already. debug mode screenshots. factorio_dbg1.jpg factorio_dbg2.jpg factorio_dbg3.jpg factorio_dbg4.jpg

Aliens can't find proper path.
They are just get stucked at the edge of river instead of flanking and find the gate.

I'm attaching the save file & mod files I'm using.