You open a Civil 3D Drawing and in one or more of your Paper Space tabs the viewports for the model are now empty (not showing any geometry). It may occur in some tabs and not others or in all tabs, and generally these are viewports that have the model space rotated in them.
This issue is almost always caused by having Dynamic North Arrows and/or Dynamic scales assigned to that viewport. If you draw anything in the viewport, then check Model Space, you will see the objects you drew are very close or at 0,0 in the Model Space Tab.
This has been a known defect in Civil 3D for a while, and still has not been resolved (it’s random and not easily repeatable).
The only solution is to reset the viewport the way you want, then make sure to explode the Dynamic North Arrow and/or Dynamic Scale bar once you have the viewport set. This will prevent this from occurring in the future for that viewport.
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