Probably a model from the Sketchup...

Yes, most likely. Around the forum there are several threads about textures and Sketchup. It is usually possible to fix with Sketchup - making sure that textures/colours only are applied to the outer surfaces (using "Orient faces", "Reverse faces" and avoid and remove the "Two sided faces"). But on a complicated model, that can be a cumbersome process.

In recent versions of SH3D, it is sometimes possible to remove the back surfaces that bleed through and ruin the rendering: If the offending material is listed in the material list (and not used elsewhere) it can be set to invisible. But then you need to be lucky with the model.

ok