Dark rings/spots in volumetric lightmap with gpu lightmass in ue 4.27

Hello, I’m moving from unity to unreal and I’m trying to figure out lightmass. I thought I had it mostly down but I found this problem with the volumetric lightmap.

I tried the same setup with CPU lightmass and it works but it takes so long It’s depressing.
The setup is an HDRI backdrop and a directional light. The skylight within the hdri backdrop is set to static.
The sphere and chair are movable.

Any ideas?