Emissive material lighting falloff regression in GPU Lightmass

Forum user noted that emissive lighting being built with GPU Lightmass is in fact being built, just not around the mesh, but in a larger radius and with reduced strength compared to 5.1.1. They found that adjusting the base color of the material finally gives me at least some light. It's very dim, base color is auto clamped 0-1. Without base color connected, there is no bounce light from emissive light.

Tested regression in //UE5/Release-5.1 and the issue was not present. This is a regression.

1. Open a blank BP project with Ray Tracing Enabled
2. Set the following in Project Settings (if not already enabled):
   • Global Illumination > Lumen
   • Reflections > Lumen
   • Enable Support for Hardware Ray Tracing (if disabled)
   • Enable Use Hardware Ray Tracing when available
   • Enable Virtual Texture Support
   • Enable Virtual Texture Lightmaps
3. Enable GPU Lightmass plugin
4. Restart the editor
5. Disable all lighting components in the Outliner
6. Switch editor view mode to Unlit
7. Create a wall using a cube and create a cylinder to place onto the wall
8. Create an emissive material and place it onto the cylinder
9. Switch editor view mode to Lit
10. Open the GPU Lightmass menu
    • Build Menu > GPU Lightmass
11. Build Lighting

Result: Light falloff from emissive material is different after bake
Expected: Light intensity and falloff from emissive material remain the same after bake