Alt-Tabbing in the Loading Screen

During the loading screen, I can usually alt tab out to do other things while the game is loading. However, that has stopped working properly. Whenever I alt - tab in the loading screen, the loading screen is still on screen, but I can tell another app is open (Excel plus sign was shown as pointer). After loading in, I was not able to move in league even though it was shown on screen, but I could interact with my computer's desktop blindly. Help?

TL;DR: When alt tabbing in loading screen, screen does not switch but I am not in League anymore