This article is the complete guide to building a stable, reliable and robust Zigbee mesh network and fixing issues with your current network and devices.
I'm saving this for reference as Zigbee has stopped working for me and I haven't had time to troubleshoot it (probably just order a longer dongle extension for starters).
My biggest gripe is that you can't tell a device not to be a router. I have some devices that just aren't very reliable, but advertise themselves as router in the network and I'd much rather be able to ban them from doing that :/