HDR backdrop


I recently export my polygons with an map channel 2 unwarp for the light map. Everything is fine in UE 4.26… Drag my fbx into my scene. Add an HDRIbackdrop with an hdri inside and after building in a preview quality, i see no difference once it’s build. Rooms with no windows or open doors should be black but instead everything, every object and different areas of the place is similar and flat.

Any idea why?