Hi John!
It picks up that it is a water sensor as noted by the water droplet icon and the controls of “water sensor” “temperature” and “battery” displayed when I hit the device in ST. In addition, I have automations that trigger when the sensors get wet that function successfully when the devices are first added.
As noted in previous responses, I have the devices throughout the house but one of them is in the same room as the hub and acts identically to the other, so…I don’t think it’s a distance problem. I think they pretty much all go offline around the same time (but I haven’t verified exactly when).