I'm generating a custom mesh out of a height map, and it works fine, except that after generating the mesh, there are a lot of duplicated vertices; duplicated in the sense that they occupy the same point in space.

In an attempt to optimise this, I run thru all of them and detect the ones in the same space and remove the duplication, and recalculate all the triangles.

This yields the same mesh, but now with 1 fifth of the vertices, the exact desired result.

However, in the unity editor, the visual changes. Some strange shadowing appears after I have optimised the mesh. See screenshots below.

This screenshot is before optimising the mesh.

This screenshot is the exact same mesh, but now with optimised vertices.

What can be the cause of this? I assume it's being done by the lightning of the scene, but no changes to the lighting has been made between the two screenshots.