The planar one at least should be rebuilt. If you have different U/V spans I'd recommend rebuilding both to have matching spans. The problem with be planar is the history attached due to construction history. The loft has it's history too, but it's more forgiving. Once you try to attach to the planar surface, odds are you break planarity and hence have no surface.

As for the render, can you post it for troubleshooting?