Hello Robert, thanks for your suggestions.
My HP23 has no Zigbee network (not any devices connected), so chances of interference between the two are very slim.
But to make sure there is no interference between the HP19 and HP23 networks, first I removed the sensor from the HP19, then I shut down the HP23 entirely, then I rebooted the HP19. After about fifteen minutes, I connected the sensor again to the HP19. The results are the same.
I included the list of Zigbee nodes. As you can see, the Water Leak sensor connects to a Ceiling Light (router) (0->6->18).
I agree that it seems extremely unlikely that there is seperate code for the HP19 and HP23. So then… What’s different? 
Just in case the router involved (this light is a Tuya Zigbee switch module) is the culprit, how would I force the Water Leak Sensor to connect to a different router?
