So, years ago I noticed ToB had a persistent and rythmic stutter on the campaign map. I found it was due to the UI, because frametimes become flat when you disable it. Now, I had played many hours already and hadn't actually noticed it, but at some point it had become much worse and I could not resolve it. I abandoned the game thereafter.

Upon reinstalling the game just now, I launched a vanilla campaign and while the stutters were still there they were not really noticeable.

Then, I installed the Shieldwall mod and the frametimes spike much higher, leading to very noticeable stutter.
It's the only mod I activated. I looked up a let's play on YT to see if someone else had the same problem with this mod, and indeed I noticed the same constant stutter.

I have no idea why this is the case or if it happens to everyone or if the mod team could even fix it. Just letting you know I singled out the overhaul as the cause of increased stutters which frankly make it unplayable to me. Very unfortunate because this mod improves the game tremendeously in every other aspect.