So it has been happening for quite some time now, since maybe the middle of February. I have already sent tickets to the support team, but none of their solutions seemed to work so far.
It usually starts off with me starting up my computer and watching some YouTube or something. Then I feel like I'm gonna paly some LoL, sign in, and then check how bad my FPS is (in practice tool). If the machine has been on for like an hour, I have about 10-20 FPS. This is when I restart my computer.
After this I sign in to League and go into a game, 120+ FPS, and with time (not that much) the FPS counter slowly but surely drops. Today I played 2 bot games (because I can't really play PvP with this issue) and the results after ~40 minutes are clear (link).
It usually drops even further and I have only experienced this issue with League.
In January for example, that 120+ FPS was constant, only dropped under when I used Alt+Tab to listen to music. Now I can't even listen to music, because it would just lower the FPS even more.
The client also gets laggy with the game.
I've got 8 GB RAM, 2 Core i3-2100 HT CPU, and NVIDIA GT740 2048 MB GPU
Checking process manager, when i start up, CPU usage is about 5-9%, Memory usagge about 20%, but right before I started writing this (all programs closed), CPU usage 15-20%, Memory usage 40-60%
Checking with AIDA 64, all temperatures normal
CCleaner has been used infinitely many times already, every single Avast and Malwarebytes scan possible has been done, all is good.
I am not even sure what may cause this problem at this point, I already found here solutions for other problems that the support team couldn't offer, so I believe you guys can help me out this time too.