The Metergroup Hydros21 isn't one of the listed officially supported sensors, but with some help of colleagues we managed to set one up and get it to report readings (Onion Omega2LTE as the controller).

Most of the time it works fine, plug in the sensor, power up the board and within a minute or so our routine is running and posting results to the web (we set it up to post on thingspeak).

Once in a while though, something gets into a funk, and the setup stops working. Power off, power on, still the same. Without touching any of the connections at all, left it powered off for multiple days, and then on powering up again, it just starts working again. What would cause this?