[UE4.26] Light Shaft not working well with Exponential Height Fog and Volumetric Clouds


I made a simple scene with Volumetric Clouds and Exponential Height Fog, and meet a strange issue when turning Light Shaft Occlusion on.

Here is the scene. Distant clouds are blended with the fog. Everything is fine.

But when the camera is behind the tree, clouds and fog show artifacts. We can see a lot of dark partterns. I guess Light Shaft affect those areas when looking from behind the tree.

So i disable light shaft occlusion, then artifacts disappear. Clouds and fog are well blended.

Actually, any object that triggers light shaft occlusion can bring this artifact. So, Any suggestion to this issue?