Lightmass Artifacts

I’m currently struggling with some artifacts that show up after building lighting with lightmass. On certain surfaces, I get these blotchy dots (other areas in the map look ok). This wall plus it’s support beams are a single mesh, and have unique lightmaps ( no lightmap errors appear after a build). I’ve encountered this several times before, usually when I have a wall piece with some sort of beams or supports on top of it. Any ideas what may be causing this?

This wall + beams are a single mesh, with a 128 lightmap. I’ve tested this with a production build and still see these splotches appear.

The lightmap density seems at least comparable to other Epic samples, like this level from Unreal Tournament. My expectation with a lower resolution lightmap density would be blurrier, less accurate baked shadows, but you can see in my example that there is a lot of noise coming through in the the bake.

This scene does make use of light portals to allow extra directional light and sky light bounce, but most of the interior light is coming from a lone spotlight on the ceiling. I am including a shot of the light settings as well

Also including a shot of the mesh in question’s lightmap UVs