Mesh generation triangles issue

Hi! I'm trying to generate spiral mesh procedurally. I'm trying to achieve it with SetTriangles and subMeshes, as each new part of the spiral should have different material. Here's what I've got so far:

For some reason newly generated subMesh triangles don't connect with each other. If I don't use submeshes and use only one material, generation script works perfectly.

What could cause the issue? Thanks in advance.

Here's the link to my script on Pastebin: https://pastebin.com/BTCJDFy9