Borderless and Fullscreen laggy

I've been trying to play some League on Borderless mode (because that's the best for recording), and I noticed that it was much much laggier than windowed mode. Whenever i moved around, or casted an ability, etc., the movement was extremely stuttery, although my FPS stayed at 26 the entire time. When I switched to fullscreen mode, I encountered the same problem; however, the problem disappeared when I played in Windowed mode. Does anybody have a fix for this?

My VSync is off and I'm running Windows 10.

(I'm recording with OBS, but it really shouldn't affect my gameplay, as it worked fine before.)

EDIT: This only seems to be a problem with 1920x1080 resolution. Changing my resolution to something smaller makes everything normal again.