FPS Lag When Opening the Shop?

I have always been able to run league at a steady 60 fps and my computer should have no issues still being able to accomplish that task. However recently (about a few weeks ago), I've been having an issue where whenever I open the shop in-game, my entire game drops to about 20 fps until I close the shop, then it raises to about 30-40 and stays there for a few minutes until it eventually fixes itself and goes back to 60. It makes playing the game incredibly annoying to play at times and it really hinders my ability to perform. Does anyone know what could be causing this issue? Thanks! I feel like the issue could have something to do with Windows 10 since this issue never occurred until I upgraded.