[CLIENT] 100% CPU usage (sometimes?)

EDIT: I mean the ingame client, not the lobby client

Hello,

so recently (since a few weeks) I've experienced an issue with the League of Legends game client (not the Lobby). Suddenly for some reason my PC fans was making very loud noise that I usually don't have when playing League. I checked the task manager and saw that League took happily 90% CPU (up to 100% by the rest of my programs) on ALL cores (not throttling though). This is framerate independent for me. If I set the framelimiter to 25 FPS the CPU usage won't differ to running unlimited on 300+ FPS. Seems like rather old fashiond spinlocks in the code, but I don't think that it should be like that. Reproducing is somewhat difficult. I didn't see a pattern in the occurences but it does happen in like 30% (very rough guess) of my games. I'm running an Intel i7 6700, with 8 GB DDR4 and an AMD R9 270X, so please don't tell me that my hardware is too slow. I mean, I've played League before just fine and never had issues with that before (it used to be like 15%-25% CPU usage in the past with framelimiter set to 120 FPS).

Well, this doesn't really impact gameplay for me, but I don't want any type of software burning CPU time for no reason on my computer and I also don't think that this behaviour is intended.

I don't have any screenshots of the task manager or so. If you desperately need some, I'll make them tomorrow. So, does anyone know what's going on and if this can be fixed?

PS: Please, as long as I'm not an idiot I usually know how to use computers, so don't reply "have you tried turning it off and on again".