Volumectric Fog causes Actors to render differently in each eye when instanced stereo in enabled. The left eye appears to render the scene correctly while the right appears to render the actors in the scene bright white (in the case of the provided example)
Result: Objects in the scene appear bright white in the right eye and are obscured by the fog in the left
Expected: Both eyes would render the scene in the same way
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-66504 in the post.