Factorio Forums

-There are large groups of biters forming on the edge of the pollution zone that seem unable to find their way to my factory

-There is a large lake between and a choke point is the closes approach

-I tried poking them with artillery and a tank but only a few enemies followed me

https://i.imgur.com/N5HkNC5.jpg

https://i.imgur.com/Tbs1aRe.png

These groups say they are created by script, so they will only respond to script commands

Most likely a mod was controlling them

Your save game doesn't contain any saves, so I can't check that