We absolutely have no way of making a faction not make a bunch of stacks and do nothing with them. No mod that I know of has the ability to make an AI faction "do" anything really along those lines. It's not an EB bug or anything like that - that's for certain.

(The only time a mod could have control over that sort of thing would be if the stacks were all congregating at a place where there was a map problem, like a needed ford or some other weird issue, and we aren't talking about that sort of thing here at all as far as anyone has ever reported.)