I have the relay attenuator plugin V1.3.0 installed and have connected a line input through the attenuator. I can play music through the input and hear it (much attenuated), but I can’t control the volume. Using the UI I have changed the attenuation from 0 all the way to 100; there is absolutely no change in the output level.
This could well be related to the other bugs that I reported, but I don’t have any way to know that. Since the symptoms are different I reported them separately.