I have a seemingly simple setup: GE Z-Wave Smart Dimmer first in line from the panel turns on/off via the physical switch as well as Smart Things App. The GE Add On Switch turns the lights on, but will not turn OFF the lights.
I thought perhaps it was a bad Add On switch, so I returned/ordered a new one and installed it tonight — still the same issue.
I’ve triple checked the current wiring against the installation instructions and it matches. The wiring is super simple: http://i.imgur.com/xeezvGC.png
I had this issue on a 5 way setup when I found power on one of the neutral’s. Once I tracked down where it was picking up the power it fixed the issue.
The Add On switch is simply a trigger switch for the Master Switch. If it is not turning off the Master Switch then it is probably the Master Switch.
GE/Jasco has reported that if you accidentally touch power to the Traveler/Trigger Contact you can mess up the switch. Even if you just accidentally touched it for a second.
Also could just be defective from the factory.
Also what @thawley22 said is true. Any power running to a neutral would disrupt how the Add-On switch triggers the Master switch.