FPS drop after some minutes but recovery after go window mode and go back fullscreen

I just changed my PC config. It is now:

I formatted the PC and installed Windows Pro. Installed NVidia drivers too.

So the problem is, I'm playing League of Legends at 240 FPS and suddenly it drops to 101-107. I check the temperature and it's 50°C. But if I just change to windowed mode and go back to fullscreen it goes to 240 FPS again for a few minutes.

I have a 144 Hz monitor so I cap FPS at 144 but it's the same - after a few minutes it drops to 101-107 but can be "fixed" with the windowed mode to full screen trick.

It only happens in League of Legends, in Overwatch, for example, I get 144 FPS all the time.

I have disabled all overlays from Xbox, Windows and Blitz (even closed Blitz).

Any ideas?

Some people that are more into building computers could correct me on this, but I think its a bad idea to run your computer to 'as much FPS than it can produce' for wear of the parts.

Especially, depending on the screen you've got, over 60 or 120FPS your screen can't even refresh quickly enough to show you those extra frames (seems you can run 144FPS, but still; I've seen lots of studies that say that except if you have an especially trained eye, over 90-100 FPS you don't see much difference).

Now, for the question at hand: Why would you drop suddenly at half the framerate? I can't really say. LoL has a history of being horribly coded with spagetti everywhere so it might just be that the Teleport animation doesnt get cleared properly and i takes a part of your CPU at all times after it's been used. And most people don't see it because they play at a lower capped FPS.

Why you seem to fix it when passing from windowed to full screen? Probably because the whole engine resets when you change window modes (thats why the screen goes full black for a few seconds when you do)

So basically: You are running 240FPS because your whole computer is giving its all. But little hiccups in the game's code start just having some elements stay to eat a little bit of ram. So little by little your FPS drops until all of Riots gremlins are at the table eating their little part of ram and that brings you to about 100-110 FPS.

So yeah, don't think there's a fix there.