AutoCAD Civil 3D

[#1]

See Attached Image - Using Conceptual View, I have hanger plates that intersect an arch, and previously where they intersect you couldn't see inside the arch just the surface. Since saving as another drawing to add hangers details something has changed in the display and the arch appears transparent at the moment so you cant see where along the plates the arch intersects. See attachment.

Unless you zoom right into the intersection, the surfaces appear and zoom out and it goes transparent again.

Ive compared the dispaly settings etc. and they seem to match up, but not dispaly the same.

Please tell me there is a simple fix for this, thanks