Zigbee is notorious for mesh instability, mostly because some devices (looking at you, Lightify) are picky about what repeaters they use in the mesh. Build your mesh slowly, spread some good repeaters around your house, and give the mesh time to settle down before using it in production. Don’t move repeater nodes or power them off. (I had some lights that I had to delete and re-add every two weeks, until I figured out that the cleaners were unplugging a repeater to plug in their vacuum:-) Finally, make use of the “Visualization” tab under Configure to see what’s happening on your mesh.