[POP UP] CompatWindow appearing on screen when LOL open

Recently, I have noticed a small white window in the upper-left corner of my screen with the text "CompatWindow" while playing League of Legends. Usually, the window pops up after 10-15 minutes of having LoL open, or 5-10 minutes into a game. The only way to make it disappear from what I've been able to do is by closing LoL. While the window is small, It becomes a problem when trying to view the HUD in the upper-left corner of my screen. If anybody has the same problem, or knows a solution, please tell me.

I took a screenshot, hopefully you can see the CompatWindow in the Upper-left corner of the picture