A limitation occurs when you import an FBX file that contains Smoothing group data into 3ds Max with the Smoothing groups option activated.
If any objects in the file contain explicit normal modifications, the FBX importer will import only the smoothing group data and ignore modifications made to the normals. For example, if you modified the normal directions, but the object also has smoothing group information.
The 3ds Max FBX plug-in does not export smoothing group data by default.