Sometimes if you compare a drawing from AutoCAD in TBC against the same drawing in AutoCAD you may find that there are hatch areas missing. In AutoCAD you can create a Hatch Area with or without a constraining boundary. When defined without the boundary, TBC cannot create the Hatch because TBC Hatches require the bounding line, so they are ignored.
If you have AutoCAD you can use the HatchGenerateBoundary command to create boundary polylines around the hatches in the CAD file and then save the DWG file and then import the updated CAD file into TBC - you will then have the lines that were missing.
Lastly - in the example here you can see that in AutoCAD the areas drawn as Solids in AutoCAD come into TBC also as Solids however they do not have the Fills that you can see in AutoCAD. For some reason when TBC imports the Solids it sets the transparency of the solids to 100% rather than 0% or 50% so the fills are not displayed. You can select all of the Solids in the project and in Properties pick the Solid objects from the list of selected objects and then change the property for Transparency to 0% and your solid fills will be displayed.
Video shows you how this works.