Basically, shaders work fine in 1.11.2. But when I use 1.12.2 and render with shaders, the render is completely broken. I've tried older and new versions of the 1.12.2 Replay Mod. And I've tried different shaders. But still, nothing works. And this is a problem because most of the shaders I use only work in 1.12.2. there's not much else I can really say about this glitch. Just check the video, it's pretty easy to tell what's wrong.
(I'm just using the default render settings at 1920x1080 at 60fps.)
Video of problem: https://youtu.be/Yskjj9BgMHM
gpu: GTX 1070
cpu: AMD Ryzen 7 1800x