How to fix dark meshes?

[BewareTheArmadillo]

Hi, does anyone know the cause and a possible fix to some meshes appearing almost completely dark after building the light? (see picture below)

You can see the ground floor on the right having the correct illumination, while the upper one and roof being super dark. (Same problem on the left as you can see)

Thanks anyone who can help!

[ClockworkOcean]

Well, it’s going to be missing or bad lightmaps.

If you double click one of the meshes, it opens the static mesh editor. There should be the UVs on the first channel and lightmap on second channel:

Generating Lightmap UVs