Try this. I can't remember what I did the last time this happened. I vaguely recall doing something like this...
Edit the DNI for the non-working device in the settings page. Add something to it, prefix with old- or whatever just so the DNI is different. Then try pairing the device again. Does it pair now? If so, you should be able to do a swap using the Swap App.
If that doesn't work, alter the Zigbee ID on the settings page to something unique (write down the old one) and see if the device pairs as a new device. Using this Iris ID on my system, 000D5F0002909D2A I would change to 000D5F0002908C1A or something like that as long as it isn't a Zigbee device already in use. Then Swap Apps if the device pairs.
This should be reversible if you re-edit the original device with the correct numbers. Just in case, I would take a backup just before messing around.
