If you have applied your materials to the back-faces, then they won’t be exported.
To check this first set your SketchUp Style to have a distinctive back-face color - e.g. bright blue.
Next view a part of your model that seems to have the problem.
With View > Textures switched on it should look OK.
Now change to View > Monochrome… if you now see lots of back-faces that’s the issue…
Materials must always be on the faces’ fronts.
Faces can be reversed using built-in context-menu tools, but there also plugins that might help to correct you ‘sloppy-modeling’…
Report back and someone will advise you further…
Perhaps if you showed us screenshots of the issue Textured & Monochrome we could advise more specifically…
One that springs to mind is available from SketchUcation [mine] - get a free membership, if you don’t already have one…
Please read its instructions carefully etc…
It works if you have textured the backs by mistake and there’s no front material etc… but there are several permutations…
Apologies for the delay, I have seen this error once again on another model, on blender 99% of it loads in correct with textures apart from a couple of textures, I have attached the Textures and Monochrome showings of the model on SketchUp