Lightmap problem with no errors

Hi to all
I hope someone helps me )

  1. I place house mesh in the new map

  1. Open mesh and look at UV in the second channel

3. Click Build and finally have no errors
4. Look at mesh in the level and was upset (

Maybe am I doing something wrong? I have no idea with correct second UV and without errors.

Additional information.
I import mesh with and after without Generate Lightmap UVs. The result is the same.

The UVs are a bit bad, by one side it has tons of empty space, and by the other side, some islands are very close one to another.

Basically your problem is lightmap resolution, the backed shadows of some islands are bleeding into another islands. Solutions:

1- Remake the UVs with more space between islands, with less empty zones and increase the lightmap resolution. (best solution)

2- Increase the lightmap resolution a lot, to compensate the small amount of space between islands.

Here there is a huge guide: Unwrapping UVs for Lightmaps | Unreal Engine Documentation

Thanks a lot, ikifenix. It helps me )