Hi dnm, yes on your original model there is kind of a mix of some areas have a solid piece for just one wall and other pieces are individual surfaces.

To get the best chance of a good transfer you would want to simplify this to make it just one single solid instead of multiple objects. You can do that by selecting the walls where each wall is a separate solid, then using Edit > Separate on those to break them into individual surfaces and then selecting just the pieces that are needed to join to each other so that you don't have any extra surfaces on the inside of the object.

Generally it tends to be more convenient to try and keep things like this as a solid more from the beginning.

I've attached a version here where I've done that and also simplified a few areas like taking 2 adjacent faces that were coplanar planes and making one single bigger plane out of them to just clean it up a little more.

Does this version transfer over better now?

- Michael