If Material is not overridden, Material will not be exported correctly.

This is because FFbxExporter::ExportStaticMeshToFbx() does not correctly determine the OverrideMaterials.

 Therefore, the following code will not pass.

else
{
	Material = StaticMesh->GetMaterial(Polygons.MaterialIndex);
}

You can also override it, even temporarily, to avoid the problem.
(2021-08-05_03h05_44.png)

1. Place the Sphere in the level.
2. Press "Reset to Default" to assign the DefaultMaterial. (2021-08-05_03h21_21.png)
3. Press "Export Selected" to export the FBX. (2021-08-05_03h13_36.png 2021-08-05_03h13_00.png)
4. If you check in MAYA, you will see that the material names are different. (2021-08-05_03h14_10.png)