I have a very similar issue, Studio One 6. I recorded a track (this is reproducible so just talking about one example) driving a multi instrument with 2 hybrid pads. I was able to listen to it a couple of times. I decided to try and change the pads it was using, and now, it is totally silent on playback, and even switching it back to the original pads doesn't resolve the issue. How can I get it to playback again?
Needless to say, I don't want to start recording things and have them suddenly become permanently mute.