[CLIENT] alt tab without pressing anything

In the last few weeks, I regularly encounter a really annoying alt + tab bug. I know from google search that alt + tab is really slow, but that is not my main problem. My main problem is that lol randomly closes down, as if I had pressed alt + tab, and I get to the desktop. In more detail: First, the game freezes for 1-2 seconds, screen and music both. Next, I get to the desktop and have to click on LoL in my taskbar to get back into the game. All in all I loose around 5 seconds, and that happens sometimes more than once in a single game, so it is really annoying and already got me killed a few times. I feel like it happens more often when I open a new window ingame (e.g. the shop or the player overview), but that could just be my imagination. And before you ask: No, I do not accidentally press alt when opening the player overview with tab...^^ Would be great if someone knows what to do there.

If relevant, I have Windows 10.