Invisible walls in UE4 after import from Sketchup with Datasmith

I have very basic model of my rooms created in Sketchup 2018 Pro, with solid walls and floor. They all are textured. I do export of this model into UE4, but then I see that many of my walls become invisible. I know that UE4 by default use one-sided faces and direction of the faces does matter. I’ve checked normal in Sketchup (switch to greyscale view mode and check if those faces are white. In sketchup wrong side of the face is shown in blue. I’ve also tried to edit geometry and do reverse side.) I see that original orientaton of my walls is correct.
What am I doing wrong? How can I fix that? Please help.

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Actually I’ve solved it myself. It seems like backface material fools Datasmith, so it can ignore (correct) normals.
In Sketchup it is allowed to assign different materials to front of the faces and and to the back of the faves. This is commonly used and is not considered as something bad. In particular I painted inside of my walls by concrete material in Sketchup and got the this result in UE4.
After I’ve painted inside of my walls by Sketchups ‘Default Material’, which means no material and re-imported the model into UE it magically fixed.

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