PROBLEM:
Model elements in a view on a sheet are visible in Revit but do not appear when printed.
CAUSE:
The Crop Box boundary has been edited.
It seems to occur when normally orthogonal edges are edited rather than just dragged.
In the example below the right end was edited rather than dragged.
SOLUTION:
Remake the Crop Box boundary.
Activate the view with the problem.
Select the Crop Box.
Hit Reset Crop button.
De-activate the view.
Do a test print.
If you still need a non-orthogonal boundary edit the boundary.
Activate the view with the problem.
Select the Crop Box.
Hit Edit Crop button.
Create new boundary sketch lines where a non-orthogonal angle is desired, leave orthogonal lines alone.
De-activate the view.