I talked about this in my latest post "[A message to Riot.](https://boards.euw.leagueoflegends.com/en/c/off-topic-en/qbxh6fHL-a-message-to-riot)". The performance of the client is just laughable. It lags so bad it's sometimes barely usable. An i5 4670 (not the best CPU, I know) should be able to handle a quite simple client. Everything takes a second or more to react sometimes, with the client taking up 80% (!) of the CPU power. I've run several stress tests and benchmarks and my CPU performs like it should do. The game is facing massive FPS issues atm.