This is the result of simple motion lighting rules. I walked into the hallway, saw the motion detector (Fibaro) blink as it reported my motion, but the ceiling light did not come on.
So, I went to the logs, and what I see is this:
Which shows exactly what I expect; the motion detector goes active, and the rule causes the bulb to be given a color temperature and level, and turned on.
Except the actual bulb in the actual ceiling isn't on. It's a Smart+ bulb, in a ceiling fixture with an old mechanical wall switch which is on.
And, when I check the device state, it shows the bulb as off, consistent with reality but not consistent with the log:
So, for a final test, I turn on the light via the hub, and it comes on (I was out of range of the motion detector, and it came on exactly when commanded through the hub web UI). (And this confirms that the physical wall switch hasn't somehow gotten turned off when I wasn't looking; well, this plus that I looked at it and it's definitely on.)
Sometimes when I walk through the hall the ceiling light does come on.
It never fails to turn on or off through the HE web UI.
This is crossing Zwave to Zigbee; my Zigbee setup is very simple, just 4 of those bulbs, no other Zigbee devices. They're connected directly to the HE. This is within the guidelines for stable Zigbee meshes in the document here, and the fact that it responds reliably on hub commands (and the other bulbs also, both manual hub commands and rules triggered by mode changes and the like) suggest that hub connectivity to the bulb is fine. If there were communications problems, I'd expect to see that in the log, too, wouldn't it?
So, I'd like to acquire a clue, if there are any available?