I see the problem as you have like 60 or more things connected to the coordinator directly. A zigbee network is intended to be a mesh, where you have a dozen ot 2 (maybe) devices on the coordinator directly and the rest connected to routing devices. So for a better network, more resilient, add more routing devices. Power plugs, bulbs that are always powered, etc in places near the end devices.
Check out some of the WIKI’s in the Cookbook list on Zigbee to explain more, but put a zigbee wall plug in each room, it will be much more stable.