Quick answer: Unity mesh detail maps disappearing after lightmap bake? Generate Lightmap UVs writes to UV1 by default - move your detail map UVs to UV2 or disable Generate Lightmap UVs on detail-mapped meshes.

After enabling progressive lightmapping, the dirt detail map on every brick wall vanished. The textures still appear in the material - just stretched into a single texel.

Move detail UVs to UV2

In the material's surface inputs, set the detail UV channel to UV2 (or UV3). The lightmap unwrap claims UV1 unconditionally when Generate Lightmap UVs is enabled.

Disable Generate Lightmap UVs

For meshes you've manually unwrapped (most artist-authored content), turn this off on the model import. Use your authored UV1 and let the bake use it instead of overwriting.

Inspect the asset

Select the imported model, expand Mesh, check UV Channels. If UV1 is generated and matches the lightmap atlas layout, that's the bug. The fix is import-level, not material-level.

“Every Unity 3D pipeline question eventually becomes a UV channel question.”

Standardize on UV0 = albedo, UV1 = lightmap, UV2+ = detail/secondary. Write it on the wiki and the next artist won't have to discover the rule via this bug.