If you’re trying to do things with lightmaps, you definitely don’t need that!
After double clicking on the mesh ( in the content browser ), you get this sort of display:
Your UVs ( which tell unreal how to position the material ) are on channel 0:
The lightmap UVs ( which the engine uses for storing lightmaps on the mesh ), are made by unreal when the mesh is imported, are on channel 1:
They should look sort of logical. If they look like a spider on speed has crawled all over the place, something’s wrong.
Having a black mesh after light build could be a number of things, including missing or maladjusted skylight, and / or sphere reflection capture.