I do have a very fine mesh. The Vertex Color is assigned, it's cleary to see when using 3dsmax.
After exporting the .fbx file and importing to Substance Painter... well, Substance Painter can't read the vertex color information.
I have exported numerous other meshes with no problem.
What's causing that issue?
Could you share your mesh? It seems to be an issue with the way 3ds Max exports .fbx. However, I can't verify that since I don't have 3DsMax on my side.