But, when I angled that same plane and ran Add Reference Plane, the output still said it made a reference plane and gave its Revit GUID (no error), but it did not show up in the same section view where I saw the horizontal reference plane.
To see the reference plane line representation in your revit views, your view needs to be in a direction parallel to the plane line as show below (left is plane, and right is the elevation view showing)
