I had a foreign invasion followed by awakening obeliskians. Suddenly, after running fine on my PC, the game ground to a crawl... time would advance a short amount and people/things would move a short distance, then it would effectively pause for seconds at a time, then move again. The UI was still responsive and everyone was still happily animating, so it wasn't simply that the CPU usage was through the roof. IIRC, the last thing I did before the slowdown was to assign a new overseer to the barracks. The previous commander died during the foreign invasion, but his NCOs were still running around and fighting the obeliskians (along with borrowed steam knights and redcoats from the empire). I assigned a new overseer to the barracks, added spare workers (which may not have been the workers formerly added to the barracks, lots of overseers died during the foreign invasion) and then I think the slowdown started. I saved and quit, and when I loaded the save this morning it still had the problem, so hopefully there's something there you can use to debug the issue.
