So recently I have been running into this problem on LoL where the fps drops to 3-4 fps. It ussually occurs if I have put the computer to sleep, and then woke it up. So, I decided to be a sleuth, and played the game with the task manager up, sorted by CPU usage. Sure enough, cpu usage spikes to 100%, but its not LoL that is eating it all up (despite LoL having nearly triple its normal cpu usage) A service called wmi provider host also spiked in usage, from around 2% to nearly 60% of my computers cpu.
So, I went into services, (windows+R then search services) and stopped the windows management instrumentation service and poof the FPS lag went away. It also happened to kill the windows security center app. So... imo, WMI provider host isn't the culprit here. I think that LoL is somehow triggering a scan by my antivirus, and wmi is just the expression of it.