On some day the game runs at my usual 75fps (I have a 75Hz monitor). Everything runs fine for the day.
The other day the game gets hard stuck at 30-33fps. Even changing the graphic settings to the bare minimum does not help. Restarting, run as admin, reinstall, graphics card update, window mode, different server, etc., nothing seems to work for me, but only on that day. The other day it's fine again.
Today, it's a 30fps day, I noticed something weird. When I tab out of the game, the game runs at the smooth 75fps, but only while in the background. When I switch into the game again, it goes back to 30-33fps.

So, is the game trolling me, or am I missing something?

Logs:
https://pastebin.com/u/DuckLyght/1/bpmEdyeL