What do you mean by “sometimes”? As far as I’m aware, it should not be possible for a single Z-Wave device to be included twice and for both instances to be online at the same time.
However, it’s possible that you didn’t fully exclude it from the controller, which left the previous node behind. I assume this is what happened.
If you add both discovered devices as things, I expect that one of them will be OFFLINE. Do not try to exclude it, as that will just remove your working node. You can instead use Z-Wave PC Controller in Simplicity Studio (previously known as Zensys Tools) to remove the dead node. I haven’t done this myself, but others have.
After you get it working, you may be interested in this:
