You've been around for more than a year and so I imagine you've seen the messages where we see a weak mesh symptom and how to cure it.
Your Routing info column found on the ZWave Details screen of Settings tells a lot, as does the Stats column. You should look for (and cure) any ghosts or devices that didn't complete the Inclusion process. (Blank Route or a Discover button)
You can follow along on the ride found in this topic:
