Texture Problem

I have this object I made in blender. I correctly unwrapped the object, added textures, baked the textures to 1 image, made a uvlightmap, but when it’s imported I get all these weird black marks. The editor shows the object completely fine like it looks in blender but when I build the lighting the object gets all messed up.

Mesh Editor: Screenshot - a93298f190a742d25d0d41fcec03d522 - Gyazo
Scene: Screenshot - 4429ff9704d9fe9b3d27226a67379d53 - Gyazo

The lightmap is set to UVChannel 1. What could be causing these weird black parts over the object?

The lightmap resolution is too low or your lightmap UV’s aren’t very good.