Some faces of Static Mesh invisible in UE4


when I export my static mesh from Blender(blend to fbx and then import the file into UE4 and drag it into my scene some faces get invisible. What’s the matter?

Thank you for your help!

This has to do with the faces and the direction they face. in Blender you have in the edit mode, than the UV tab, a button for flipping the direction of each face. Highlight the affected area and click flip direction, do this for each face with an issue than hit the recalculate button, and this should fix it.