What material do you have on the ground plane?
Any material. I attach a short video and the 3dm.
SOLVED. I created some simple curves on the surface I am using as a ground plane and they rendered which displays the same problem when rendering the ground plane block-instance.
I then checked RhinoGold/Render/Render Settings/Wireframe (Rhino 5.0/Document Properties/Brazil/Wireframe) and found the checkbox for Render Curves was enabled by DEFAULT.
I unchecked this setting and it solved the problem. The "block-instance" of the Ground Plane must somehow have CURVES grouped/embedded somehow?? Anyway that has solved the problem. Not sure if this is a bug with the block instance of the ground plane and therefore this is a work around but it resolves the issue for me.
Rik - Sydney