There are three GameObjects in my scene (screenshot below). The two "Grass" blocks are the visible ones parented to an invisible GameObject "grass" which has a CombineChildren component script.
A point light is illuminating the scene, but it does not distribute the light evenly over the two blocks (there is a visible "light gap" where none should be).
Is there a way to fix the lighting?
Editor screenshot
I think the normals of your cubes are wrong. Try it with the buildin Cube object and see if the problem disappears.
The normals looked fine in Blender. But exporting the cube into a different format (.dae in this case) fixed the lighting apparently. I'm guessing Unitys .blend importer (or maybe even blender's own file format) is bad.
Sorry for the Necro, but this came up in a Google search for the same problem that I was having, and after reading and experimenting, I came up with a solution.
In the model’s import settings (Mine is also a cube, just for experimenting) under Normals & Tangents, I changed Normals from “Import” to “Calculate”, and it smoothed right out.