Hi,
PBRMetallicRoughnessMaterial is extending PBRBaseSimpleMaterial that is extending PBRBaseMaterial.
Inside PBRBaseMaterial there is protected property for lightmapTexture but its not exposed inside PBRBaseSimpleMaterial so lightmapTexture can not be used with PBRMetallicRoughnessMaterial.
Is that by the design that metallic pbr doesn't have lightmapTexture ? as it is exposed only for PBRMaterial right now.
Thanks