In-game freeze glitch?

Ok, soo, first off, i play in 1920x1080 borderless fullscreen, which riot ALWAYS BREAKS, EVERY TIME there's an update. but thats not why im here.

recently, while playing, doing what i do, i occasionally tab out of the game to swap music on firefox/youtube. But strangely, sometimes, the game just.. freezes, when i tab back in. and i don't mean 'not responding', it runs perfectly fine when say, discord is tabbed in above it. Whenever i tab back into the game, everything freezes, and my only options to fix it are to restart the client. which can, in pvp, be a serious problem.

Any fix ideas?