I’m going to ask the obvious question, is there a buffering device within about 15ft of the lock? That’s a good way to cover your bases to start with since most mesh/timing issues can be resolved with this 
Apart from that other things to try:
- Check battery, on this model 60% is a good time replace it below which we start seeing trouble with lost packets/communication. Anything below 50% and it can suddenly shut off due to load voltage drops. Always helps just to test with new batteries.
- Try to power it down and power it back up
- If that doesn’t work maybe try to factory reset the lock, this mean you’ll need to exclude and pair it again with SmartThings. Since you’re getting notifications it’s unlikely you need to do this far but as a last option
Since everything else is working I’d wager a timing issue. Maybe try to reboot the hub and internet router if that’s causing latency related timeouts (unlikely but never hurts).
One good thing to check it the routing. Open the IDE, click on My Devices, click on your lock and see if the lock is connecting directly to the hub or through other devices? If it’s directly then I’d back to the first line. If there are other device, check if any of them are malfunctioning, maybe take them offline and do a network repair and see if that helps.