BSP to Static Mesh 3D models are see through / missing default textures?

When one creates a 3D object using various BSP brushes and combining them into a static mesh using small measurements for each BSP piece it frequently makes the BSP see through in some places on the completed mesh before and after converting all pieces to a static mesh on unreal 5.1.1. This does not only happen when subtractive brushes are used but when smaller additive BSP intersect it also often creates the see through problem along the intersection point. There is no reason there should be holes or see through parts in BSP to static mesh 3d models so does anyone know why this happens? Here is an image of the issue. Imgur: The magic of the Internet