Windowed/Windowed Fullscreen 6-10 FPS

I installed the game recently and played with Windowed Fullscreen (borderless) for a while and observed some choppiness. I went to fullscreen and everything was fine. However, I'd like to go back to borderless to make some plugins work. Whenever I do, I now get between 6-10 FPS even in the menu. If I click around too much it crashes. This happens in windowed as well. I've tried removing all overlays, playing with all settings, etc, but nothing does it.

I got i5-8600k and 1080TI. Usually my framerate is above 150.

Any ideas please?

Edit: Seems like there's an issue with G-sync when it's enabled for both full screen and borderless. It used to work just fine in previous expansions.