It was partly the GUI.
A simple user mod, available and functional on Steam workshop IIRC (so not a "hack", it did not even need that far into the games code)... FIXED it!
So the users were able to fix things the coders were not. Similar happened with KSP, but the coders eventually fixed it. Basically a lot of coders forget to limit FPS render on GUI, or alternatively checkerboard/raster calls. So you either have a GPU going "this is sooo easy, I can render 4000 frames a second for this" and the games render engine falling over as it actually tries to deliver those :P or you end up with the GUI trying to call 4000 entries on every pixel/button/line/fade of the GUI because someone forgot to stop the recursion at 4 (or render everything out to a bitmap and making 1 call to that bitmap instead).
I might be slightly wrong with the terms, but it seems to be recurring problem. Halo:MCC does the same, but only for some people strangely. And no, it's not the windows version, as it bugs out on some of the Xboxes too!!!