I had the problem of the door unlocking on its own several times a week in November 2015, as I reported in the forums. I worked with support on it for over a month, including with an engineer, and we never did figure it out. It showed up in the logs, but there wasn’t anything causing it.
This was a regular Z wave lock using the stock DTH. This was a major safety issue for me because my service dog knows how to open the door handle, but not turn the deadbolt. So he is trained that when the deadbolt opens, he should go over to the door and be ready to open the handle if needed.
I was very concerned that the door would unlock unexpectedly and he would let himself out.
After we weren’t able to resolve the problem, I ended up taking that lock off of SmartThings all together and using a different Z wave controller and have not had a problem with it since. So I’m pretty sure the problem was SmartThings, not the lock.
This is a rare problem, but it has happened to some people, and not everyone has been able to resolve it. So I’m not really sure what the next steps should be.