I had a supply air system that was at 15'-0" or so AFF... I moved the duct system down to about 12'-0" AFF but when I did so I "lost" all of my flex duct. On my plan view, the flex duct is clearly shown in single line. However, when I go to my 3D view (or export to navisworks) the flex duct is NOT there.
What is odd is that when I moevd the system down, some of the flex duct did update and redraw, others did not. I even went back and deleted the flex on plan view and re-drew it... still with no luck!
To help the community get a better idea of what you are seeing, a small sample file, with screenshots would help give a better picture of what you are seeing. If you can get the file down to a few ducts and terminals, you can post it on this thread.