I am sorry that I have not mentioned about the the function of the button. It only have one function. That is to reset the module. Once you do that during the start up, all configuration on the device is cleared( factory reset). It will never connect anymore until you remove the device on your hubitat. The button does not work like Xioami's where they may have multiple functions.
Now that is out of the way, I have tried to shutdown my modules and reconnect after 15 minutes in the past. I do not remember whether I did that with ST or Hubitat. I will pay more attention now with Hubitat and see if I can reproduce the issue. I will compare also with ST behavior. I will let you know what I find.
I will note this behavior. I had issue in the past with Bosch devices. In this case, I found the Bosch went rouge. Every zigbee device is assigned a 16bit network id. The bosch at one point keep taking over the 16 bit network id of my module. Yes. It literally send packet using the network id of the module. The module zigbee network layer detect this condition perform conflict resolution. It does leave the network and rejoin the mesh. I found while connecting to ST. ST allow the module to come back without manually do the join process. I found this problem by looking at 16 bit network id. The module network id keep changing every couple hours in ST ide. To troubleshoot this issue, I have to use Zigbee sniffer. I rebooted the Bosch. The issue went away. I can never reproduce the issue.
I mentioned my finding above because that is the only instance I can recall the module get kicked out of the mesh. In ST, it was able to re-joined and assigned a new id. If I do have the time, I will try to get the water sensor. However, if my suspicion is correct , there is nothing the module can do. If a device in a network steal its network ID, it will leave the network. This bring to a point related to your first issue. It seems like the module is not allowed back.
Thanks for this suggestion. Let me think about it. I do get opposing suggestion. Some people do not like blinking led. Keepin the sensor anonymous is also an advantage for some people. They just want the sensor to be tucked in some corner and not calling for attention. I do hope to have some kind of device health feature. This will get the job done and more discrete.