I am experiencing a similar problem to what's been reported previously. I have a 3d sphere in my compostition that is lit with the light falling off. When I render it, the light falloff changes to a harsh edge.
I had been previously told by Adobe that this was a known problem over 6 months ago, and still nothing has been done to correct it. What gives?
This forum is answered by volunteer Photoshop users. We do not work for Adobe so have no knowledge of future fix dates.
That said, I've not seen any bug fixes for 3D issues in Photoshop for a long time. My recommendation would be to use a full 3D application for rendering. If you have the full CC subscription you could use Adobe Dimension. If not, you could use Blender, which is very powerful, has fast rendering on the GPU and is also free. You can always bring the rendered output back to Photoshop for compositing with the 2D elements of your image.