I updated Windows 10 to the latest version last night and also patched League and I noticed that in game, I never get more than 60 fps (even though I always play on capped 144 with no problem) and I'm having a lot of frame lag and horrible frame drops every time I get into a team fight. It's definitely not my computer seeing as how I've never once had a problem with frames other than when my computer overheats (which it's not)
It's bad enough where I spike between 10-60 fps every time I move, the game is unplayable right now.
EDIT: Completely uninstalling and reinstalling the game fixed the issue for me!
EDIT 2: Well, that was short lived, it's doing it again. >_< Reinstalling didn't help this time. :(