Mesh was imported without them, and had auto-generated UVs, now that I reimport the mesh, the engine just doesn’t see them. I looked everywhere, there seems to be no settings that tell the engine to finally ditch those lightmap uvs and use the ones imported with the mesh
You have to set the Lightmap Coordinate Index in the static mesh editor panel to the number of your corresponding UV set and you would also need to uncheck generate Auto Lightmap UVs in there.
That said Lightmaps are very buggy at the moment. I myself also had the bug that prevents the setting of the Lightmap Coordinate Index from 0 to another number, It seems this has with the LOD generation in 4.24.x to do.
The Index is set correctly, the engine sees and uses the lightmap UV’s however it wont replace the auto-generated ones with the imported ones, if at first Lightmap UV’s were generated. Even after you uncheck the auto-generation. it keeps using the engine lightmap uv’s.
Moreover, I deleted the fbx and the UEasset files from the directory (but not from the scene) then freshly reimported them, and the engine still managed to overwrite (or that’s what I think happened) the imported Lightmap UVs with the ones that were on the scene meshes. (yes I did delete them and repopulated the scene).
Only by deleting the asset from everywhere was I able to finally bring in my Lightmap UVs