AutoCAD MEP 2015 HVAC Duct Disappeared on Drawing!

by Cheryl
(Louisiana)

Has anyone ever experienced this issue?

After finishing the duct runs for a project, using the MEP tool palette, I started to create section cuts utilizing the Vertical Section tool.

It worked fine but when I went back into Model Space to create another section MOST OF MY DUCT WAS MISSING!

The fittings are there, most of them, anyway. If I go to Paper Space though, THE DUCT SHOWS UP IN MOST OF THE VIEWS!

All Layers are on, thawed and unlocked. I even hit the UNDO command to go back to before the Vertical Section command. GONE!

Here is the strangest part... I go to an older backup file and try to copy/paste the duct in and THAT doesn't show the duct either!!

It is obviously some type of setting that chose to reset itself randomly, but I have no clue HOW to recover 4 days of work!!

Can anyone offer suggestions?

Thank you in advance!
Cheryl