Do you have two zwave hubs on the same network? If so, and smartthings is the secondary hub, it is normal that smartthings would only be aware of the devices that were present on the zwave network at the time that the SmartThings hub itself were added to the network. It will not be aware of anything added by the other hub after that time. It’s just the way it works when a hub does not support controller shift, and smartthings does not.
To pick up the new devices, you have to remove the Smartthings hub and re-add it, and then it will be aware of all of the devices on the network at the time that it rejoins.
There are other brands of hubs, such as Ezlo/vera, which do handle this differently. But they aren’t required to by the Z wave specifications, and SmartThings does not.
The following community FAQ explains in more detail:
FAQ: Zwave Secondary Hub Basics
If I am misunderstanding, and the smartthings hub is the only hub on your Z-wave network, then that’s a different issue. 