I see this is an older post and you've hopefully already fixed the issue but... This looks like you are drawing over an Xref'd PDF? If so, in the model space, click on the PDF and open your shortcut menu, click "Draw Order" and then click "Send to Back". I run into this same issue often for some reason when I've changed the view via Orbit, rather than using the standard View Controls, even though I always make sure the pipe or duct I am modeling is at an elevation above the elevation the PDF is referenced in at.
