I didn’t find any sections in your model.
This is what the DWG file you posted looks like in DWG TrueView:
It is what you get if you export a section slice: a 2D cut through the model, with no other things.
Get rid of all the 3D Warehouse junk. More than 11 million edges for a house model is ridiculous. To export this to DWG (2D view or 3D model) will take a very long time, overnight perhaps.