I tested this on a Mac Pro in UE 4.15, 4.16, 4.17, and 4.18. As a possible workaround for the fog issue, I've discovered that setting Atmospheric Fog > Lighting > Disable Ground Scatter to "True" will prevent the fog from rendering black in editor.
I got some issues with my translucent materials on MacOs devices, this issues appears on packaged builds and sometimes in Play In Editor (But usually, in PIE works fine, except the atmospheric fog that is always black without opacity).
The translucent area appears to be black or pink, depend on the level that I'm on, also, it happens the same thing with the Atmospheric fog of Unreal
I tried changing the r.TranslucencyLightingVolumeDim (that solved some similar issues on PS4 builds) but without any luck
That happens with all my translucent materials and particles
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-53720 in the post.