The most common mistake concerning this is to forget that the bus will ignore any RTPC that is set for a specific game object.
Make sure that no game object was specified when passing the RTPC to the engine so that the Bus will consider it.
Why does the bus has to ignore RTPC that are game object specific?
It is because when a bus applies parameters, it may be after having sub-mixed multiple sounds that were associated to different game object.
