Global Fog problem on OpenGL

I'm encountering an issue with unity's global fog on 5.6.1f1 on OpenGL. I did a bit of searching and didn't come up with anything so forgive me if this is a known issue. Here's a screencap of what happens when I have GlobalFog.cs attached to my camera and look downwards with my FPS controller:

I have both distance and height fog selected - but if I deselect either of them the artifacts go away. I feel as though this is an openGL issue however, because when I open the same scene with Metal (macOS) instead of OpenGL it works fine. I'm a shader newb so any help would be greatly appreciated!

 

Try Stylized Fog from unity lighting sample :
https://www.assetstore.unity3d.com/en/#!/content/73563