This took me a while to figure out!
I'm on the latest version osx using a line6 ux8. On the first load of Audiomulch I can set up a sound in contraption and connect it, but no sound will come out until I double click on it to open it. If I start a new scene everything works as expected.
Line6 was terrible drivers so it's probably their fault and it's not a huge issue. I'm just posting in case it helps someone else.