Ok dang, so the ZEN16 has no useful neighbors, just the hub. The other neighbor is a battery Zooz switch, guessing a ZEN34. It does seem they can route through non neighbors when times are desperate, which is what it has been doing when it re-routes.
Could you get a device on the inside of the house between the ZEN16 and the hub? Ideally closer to the ZEN16 I think. Maybe a ZAC38 could go somewhere and also it would give you the ability to detect power outages? [DRIVER] Zooz ZAC38 Range Extender (and Power Outage Monitor)
You could benefit from a denser mesh, seems like your devices are either spread out a lot, or something in your walls is interfering. EDIT: I just realized you said up above it is 50ft from the hub on a fence. Whatever devices are between it and the hub, seem to be too far away or too weak for it to communicate with them. Any chance of getting a repeater closer to the ZEN16?
