When the node itself has no material, the material will not be applied to the node after the following code is executed to assign a new material to the node and save it.
Scene scene = Scene.FromFile("test.fbx");
Node testNode = scene.RootNode.GetChild("test");
testNode.Material = new PhongMaterial("newMaterial");
scene.Save("newTest.fbx", FileFormat.FBX7500Binary);
Can you please share the sample FBX file in .zip format with us? We will investigate and share our feedback with you accordingly.
An investigation ticket as THREEDNET-1268 has been logged in our issue tracking system to further analyze this case. We will look into its details and keep you posted with the status of its correction. Please be patient and spare us little time.
We are sorry for the inconvenience.