When inserting dwg files, simple rounded objects desappears!

[rbarbosa8DQGJ]

My dwg links inserted on Revit does not show rounded surfaces, such as tubes or solids rods, extruded or sweeped. What should I do?
In the image, the tube in the railing exists in dwg but do not appear on Revit, after insert as a link.
The original file already is dwg autocad format. Even though, I tried to export or save in 2018 format. No success... The result is the same, after that message.

 It is a sad news. We have a large number of existing equipment and auxialiary structures wich must be used as "external references", to use autocad language... We would not to be happy to redraw 3D elements which alrealdy exists in other 3d model. It seems to be a rework to be avoided, since we need to focus on modeling new structures and new elements. Also, this large file size are a huge problem to the final file, once we have to export Revit to dwg, since is a client´s demand. Those exported dwg files are huge, specially when we need to save in previous version of Autocad... I will definitly open an idea to demand solution for this issue. 

ISC Plataformas - NIVEL INFERIOR.dwg

[bill_gilliss]

I have experimented with your PLAT 1, PLAT 2, and PLAT 3.DWG blocks, and think that that the problem might be with how the railings were created. First, I verified that Revit is indeed able to import solids constructed by extruding a circle along a continuous filleted 3D polyline, as shown below, so that is not the problem.

I found that I sometimes needed to stretch the vertex of one section of the polyline to make it snap to the endpoint of the next section before AutoCAD would join all the sections into a single 3D polyline. Maybe your railings were created in sections and unioned, with slight inaccuracies at the joints? Try to rebuild each one as a continuous 3D polyline -- or don't union the separate sections.. That's all I can think of. Good luck!

[rbarbosa8DQGJ]

I used sweep to create those parts. I used that command for represent tubes and rounded rods. I think the problem might be with sweep command... that is bad, because create tubes with extrude is not that easy...