This is typically a failure of the status message to get through. Or it can be a defective lock. But more commonly a range issue.
Zwave locks use a special kind of repeating message. Because the manufacturers don’t want there to be any delay while the person is standing there waiting for the door to unlock, but they also want the batteries in the lock to last as long as possible, the repeater which is closest to the door lock is supposed to keep sending the message until the lock wakes up and hears it. This is a different kind of repeating than anything else in a zwave network. But it will only happen if the neighbor which is closest to the lock supports beaming. Not all repeaters do.
So the first thing is to determine if you have a mains-powered device which supports beaming within about 8 feet of that lock. (Battery powered devices and smoke alarms do not repeat, do you can skip checking those. Typical repeaters are light switches, wired relays, and plug in receptacles.)
http://www.z-wave.com/find_products/lighting
You can look this up by checking the devices “conformance statement” on the official Z wave alliance website. Make sure you check the exact model that you have, as this feature is not present in all devices.
If you do, then you should run the zwave repair utility to make sure that all the address tables are up-to-date. You may not see results from the repair for several hours, as the tables can take a little while to rebuild even after you get the message that the utility has completed. But you should see an improvement the next day.
If doing the repair doesn’t help, or if you need help doing it, contact support@smartThings.com
if you don’t have a device that supports beaming close to the lock, try moving one to that position, then run the repair, and see if things are better the next day.
The following two articles explain how to do the repair utility, and a little more about range.
If by chance this is a zigbee lock, the beaming requirement doesn’t apply, but it could still be range.