What cause black spots on my static meshes?

After building lighting I get black spots on my mesh.

You can see it on the corner here. Tried a few things to fix it but had this problem ever since I started using ue4, any ideas?
Heres what the uv looks like

In blender, set your mesh shading to flat

then in UE4, when importing the model, import the normals and the tangents with it.

Hope this solve the problem, good luck with your projects.