Having a clipping plane active in a model doesn’t automatically give you the clipped geometry but the full geometry.
Clipping planes in Rhino are handled in-display, meaning that essentially OpenGL shaders determine when to draw geometry or not.
For Raytraced and Rhino Render (together RhinoCycles) a custom clipping plane solution has been implemented, where ray hits are checked against the clipping plane and rays get adjusted to account for that clipping plane. The geometry received is still the full, unclipped geometry. Currently RhinoCycles does not render fill surfaces. I did write a utility function that can provide those, but I’d still need to get those through the ChangeQueue properly annotated as fill surface (so special handling in clipping plane code can be done).
To recap: all our display modes receive the full geometry and handle the clipping rejection during the drawing.
It should be possible for the creators of Enscape to find a working solution with the current setup.