We've also been hearing reports that mods which pause the game on load have been adversely affected by the recent 'Paradox Launcher' update. We've been getting some reports that new version of Transport Lines Manager (TLM) v13.1, I think?, has introduced some lag please let us know if you use or don't use that mod so we can get better idea if it might be the culprit. Improving performance of those things is a staggeringly complex task which will take a lot of time those features can be turned off in the 'Maintenance' tab of our mod options screen if you want to reduce performance impact. The other fps impacts, which will get worse as the city grows, are due to things like timed traffic lights, priority signs, advanced vehicle AI and DLS (dynamic lane selection) however even these shouldn't impact fps as much as being described. We will hopefully have those issues greatly reduced by, roughly, version 11.3. speed limits or vehicle restriction icons) the overlays can cause very noticeable lag and 'stuttering' of camera movements. The biggest fps drops that TMPE currently causes are when tool overlays are visible (eg. TMPE does cause some lag (always has) but only once did it ever cause fps drop like you are describing - a bug that caused per-frame debug logging while train tracks were in camera view, and we fixed that a few hours after users alerted us to it.

We had about 13,000 beta testers while v11 was being developed (the version that's currently on the v11 STABLE workshop page) and there weren't any reports of adverse impacts on performace there.

Cities skylines tmpe fps drop