That would the SmartThings “Device Health” which is marking it offline. The way it works is that ST “pings” the lock from time to time. If the lock responds to the ping it marks it online and if it fails to see a response it marks the lock as Offline. It doesn’t mean there’s an issue with the lock (as you’ve seen when you try to lock/unlock it), it just means that the ping/response from the lock didn’t reach the hub. This often means there’s an issue with the Z-Wave mesh because of which some messages are being lost.
A few best practices when using a lock to avoid such issues:
- Have a buffering device within 20ft of your lock
- Reboot the hub and do a Z-Wave repair
- Ensure your lock batteries at strong, especially with Schlage deadbolt locks, they tend to start dying around 75% which can interfere with it’s mesh communications. See this post for more details: At what percentage to change batteries in Schlage lever lock? - #12 by RBoy