The error is the UV’s on the imported meshes are overlapping on whatever channel is specified for lightmaps, i.e. the faces cannot overlap in the UV editor. Default index for lightmaps is 1 where slot 0 is texture UV layout. Look for “light map coordinate index” in the mesh viewer details for the meshes with errors.
The mesh should be exported with two UV sets to use defaults described above. Easiest way to do UV’s for the lightmap layer is just to auto unwrap in maya/max and re-export and it will be fine after that, just verify the map coordinate index for the mesh is set to the UV channel that has the auto unwrapped UV’s