I am finding it is possibly exacerbated by cheat commands. Which is frustrating as it means I wasted about 30 games of testing, I only used it to watch what they were doing I tried a bunch of AI mods & it happened with all bar one of them (a 2016 Nightmare WinCond for Exp AI - that gave massive resources & full LOS to all AI)
It seems to happen if you stop, as in if you stop attacking & say defend 1 or 2 choke points, the AI will stop & not even fire a shot. It wont even enter the area. The 179 units mod seems to be unaffected, My Angriff series of mods are, as are many other tuning packs. I tried replacing the AI files that I guessed had been used, around 12 of them, it still did it... that irked me!
I am doing most of my test to date on the first map I linked, as that shows it up very well. I was using that map & trying different mods. Today I will do more vanilla testing with different maps & see if I can nail it down. I played until 2am last night working on this. Wife is getting pissy.
I vaguely remember other patches breaking things in mods or modding tools. I don't remember the specifics, but think I read it in someone's update notes on one of the mods that I subscribe. I'm glad the 179 units mod isn't affected because that's probably my favorite for comp-stomping. Good luck in figuring this out.
My wife gets pissy about COH as well......