What resolution? That’s exactly the point!
I have no idea what lightmap resolution ue4 wants for LODs! Because there’s no control for it! Or none that I’m aware of.
So I have to just guess blindly. Even then the results can be ■■■■ when unreal decides to make lod2’s lightmap resolution so low its shadows turn into a formless blob. And its extremely noticeable, casing so-called “lod pop-ins”.