The visualization of the Motion Controller Component Visualization as described here Motion Controller Component Setup | Unreal Engine Documentation (section Motion Controller Component Visualization) does not display the actual material of the controllers in a final build but instead uses the default world material (grey checkers). When testing inside the Editor the controllers have the correct material though so I guess the material is not being included in the final build.
Think this is a bug but if anyone actual does have a working version, please let me know.