Please register for Total War Access to use the forums. If you're an existing user, your forum details will be merged with Total War Access if you register with the same email or username. For more information please read our FAQ’s here.
It would seem that if you spread your armies wide enough across the map, with some units hidden, you can trigger the AI into a loop where it just keeps repositioning its armies and creating large blobs. I think what may be happening is that when the AI repositions one way, some opposing hidden units are revealed which causes the AI to reposition again, opposing units then become hidden, and AI once again repositions, ad nauseam.