I have similar problem in the past. In my case, I find that I have a rouge device that send packet with short Zigbee NWK ID of my router.
I found this issue by sniffing my zigbee packets. Zigbee packet is encrypted. But, to track this issue, you do not need to decrypted the packets. The packets will print the 64bit mac address and the short address. When the router change ID, i notice a packet with the same short NWK ID with different MAC address.
In Zigbee, there is a mechanism to resolve conflicting addresses. This mechanism kicked in when the router receive a packet with the same short network id from a packet that does not have the same mac as its own.
My device that generate this packet is a Bosch Motion sensor. From my observation, it start doing this when it is low on battery.
I am not sure whether you have the same issue. This is what did happen to me.
