I know you have already returned the lock and got a new one, but just in case this will help someone else…
I had the same problem - my Schlage Camelot lock worked with my v2 hub to unlock/lock for a few days and then it stopped working. I think it had something to do with manually unlocking and locking the lock because after doing that, I was unable to unlock/lock from my iOS app since it could no longer get the correct status.
So I force deleted the lock from my Things so it no longer showed up on that list and then I tried to add it back to the hub but it could not find the lock again. I tried to exclude it from the app via My Locations -> Hub -> Z-Wave Utilities -> General Device Exclusion but it would not get excluded - every time I push the Schlage on my lock, enter the 6-digit programming code, and press 0, I would get the red X instead of the green check. After many unsuccessful attempts, I happen to notice that my lock was still showing up at https://graph.api.smartthings.com/device/list but it had the status of Removed. I clicked the link for my lock and tried to Delete it, but it would not let me, saying that it was In Use. Then I noticed at the bottom of that page where the Edit/Delete buttons are, it showed the SmartApps that were using it. After uninstalling that SmartApp (for me, that SmartApp happened to be IFTTT), I was able to exclude the lock and add it back to my hub.
After adding the lock back to my hub, I thought it was still not working. But it turns out I have to wait about one minute and then it started working again; I was able to unlock and lock from the app.