Getting random FPS stutters on Mac since patch 8.12 or something.

I'm on El Capitan. Every single game I play is absolutely fine. LoL all of a sudden has weird visual stutters every time I move the camera around. What's weird is that the FPS counter remains at a solid 120 or so. I'm dualbooting Windows 10 and my W10 installation runs perfectly fine, so i have to reboot every time I want to play a game of LoL… Help?