I export mesh (f.e. door) from Sketchup Pro 2015 (imported from warehouse) to Modo 801 SP2, newest Blender, AccuTrans 3d (converter) as dae, fbx and obj. I tried it on many different meshes. Every time I import mesh from Sketchup to other software I have got missed faces - mostly n-gons but quads also. I`ve tried clean mesh scripts. In every software is almost same situation - few missed faces. All faces in Sketchup are one color so I suppose that every face are oriented well. How to fix it? How to avoid missed faces during export?
Could it be face normals? SketchUp is very forgiving in terms of front and back sides of faces - but other software tend to be stricter and only render the front side.
If you turn on monocrome shading for faces under Styles and set the background to red for instance, do you see the backsides facing outwards? Do they match the missing faces?
Other than that stab in the dark, can you share a sample model?