Audio Master in Matinee doesn't work?

I have this scene where sounds are activated via blueprints, and others are just attached to objects. I’m trying to fade in the sounds at the start of the level using Audio Master in Matinee (inside the director group) but it doesn’t appear to do anything. I placed keyframes with different values and even checked the graph, and everything looks normal. Is this a bug or am I missing something?
Thank you