I was getting really frustrated with not being able to get Door Unlock notifications but I think I found out what was happening.
On my Lock Device I had "Enable Lock Encryption" enabled. As soon as I disabled it everything started working just fine.
Hope this helps someone.
I would post a screenshot, but I don't seem to have permission. 
Edit: well, it's the next day and it has stopped working again. I don't think "Enable Lock Encryption" is the problem any more.
Also, Maybe Related: Kwikset Smartcode 910 Zigbee Not Recognizing User Code Entered
