Normal FPS(100-150) but feels like 20 since this patch

Try turning of "Memory Integrity" on the core isolation page in your settings, It works for me. I've been loading in late for the past month and just yesterday started having terrible lag/freezing that was unplayable in any serious game. https://imgur.com/a/KjHU3B3

Hopefully if its on that works for you.

https://support.riotgames.com/hc/en-us/articles/209010626-Frame-Skipping-on-High-End-PCs

Same