Ok, so this has been happening for a while now (approx 2 months) and I have no idea what it is...
I have tried updating my drivers and reinstalling LoL but nothing works. Sometimes I even have to restart my PC. This issue is really frustrating, especially when playing ranked.
Here's the log:
I run the game smoothly with 100+ FPS and 20-30 ms
**EDIT: I think I found a solution to the problem!**
1. Search for "Indexing options" on Windows (Also exists in control panel)
2. Click modify and uncheck the folder that starts with csc://
4. Click advanced and then click "Rebuild index".
5. Wait for it to finish and restart your PC.