Same here. Any clue what's happening or how to fix it?

I can at least say that's not related to the mod. It happened to me a few months back playing totally vanilla. It bites but if your army's not in the settlement, the game treats your own army as reinforcements or something. So it's best to keep your armies within the settlements of Looter territory where the Looter spawns can attack in the same turn they spawn in.

yea this is a known bug ca never patched. I think it effects multiplayer more often than singleplayer. i dont think ive ever had it happen in singleplayer.