I’ve run into this issue on two separate projects now. I’ll create a Sky and Fog Volume, a new settings profile, and then set up the fog how I’d like. Everything works great and even survives a full lighting bake later on (usually I have to continually tweak other things, but at least the fog doesn’t just up and disappear).
Then, I’ll save, close unity for the day, and come back again later.
Here’s the settings panel on a brand new project:

And the fog settings on my project after reloading:

Nothing in the project settings change, it literally just takes me saving, closing and re-opening. It’s not every time, either - just at some random point, the extra settings go away and never come back.
To make matters worse, all of the volumetric lighting and volumetric fog disappear from the scene entirely. This even happens in the sample scene, too.
From the fresh project:
From the reloaded (bugged) project:
Can someone provide a hint at what’s changed?
Version: 2020.2.2f1.3859.13 Personal
Revision: 2020.2/release 068178b99f32
Built: Tue, 19 Jan 2021 14:07:33 GMT

