Hi, we have this issue.
We use MeshStandardMaterial in our project as main shader type.
I faced this situation where lightmaps are nicely shown in materials that have a light color and no metalness.
When I turn material darker, a light goes dull and it takes too much color from the actual base color.
If I introduce metalness, lightmap disappears even if surface roughness is close to one.
Should we use different shader types for dark materials? I also tried to boost up the lightmap intensity but it just messes up the overall look.