I'm running Iris 1.7 with Distant Horizons and a compatible shader. Whenever I bring up ANY sort of UI menu, my FPS gets extremely low. As soon as I leave the UI and return to normal gameplay, the FPS returns to normal shortly after. I've disabled DH and only ran the shader, and the problem persisted. I tried again with the shader completely disabled, and the problem was instantly resovled. Interestingly, I've noticed the problem doesn't seem to occur with the F3 menu open.