I have two Sonoff SNZB-02 temp/humidity sensors for a year now, one in my bathroom, the other on my back porch area. The one outside is more than covered enough to not get rained on. The one in the bathroom is there to turn on the vent fan when the humidity goes up, so steam from a shower, and later turn the fan off. The one outside is just so I have a local thermometer and hygrometer (humidity).
The one in the bathroom has worked flawlessly, and still has the original battery that as of 7 seconds before posting this, is at 80%.
The on on the porch has simply stopped reporting twice, and I've had to delete it and re include it. Also, I've had to replace the battery twice, and the current one says it's at 37%. But, I checked the battery with a multi meter, and it's at a healthy 3 volts. EDIT After I posted this, the battery started showing 42%.
I know these things are listed for indoor use only, but being on my back porch where it never gets sun or wet form rain can't be any worse than a bathroom that gets nearly London fog conditions on a daily basis.
I can only suggest checking and probably cleaning or bending a little the battery holder metal parts that make contact with the cell, these are not always of the greatest quality ..
You could look at your ZigBee logging in the settings and search for the lasthoprssi for your device. I have currently a value of -56. Nearer 0 the better higher value the worst. It is somewhat a indication of the amount of power used to transmit the data. If the value is too low, this is a clear indication that a repeater is needed.
This is assuming that the battery contact is good as suggested by @kkossev .
What temperature range does the porch sensor experience? Anecdotally, I found these to be fine for indoor temperature range, but to become flaky with very low temperatures.
If you are able to re-include it without deleting it first, you won't have to re-add it to all your automations. Doesn't help the underlying problem though!
I find those symptoms are indication the sensor signal is in the fringe. You could try exchanging the 2 devices to find out if it's the device or the location. I have tried what you are doing with these sensors and gave up. You can calibrate the sensor to the indoor temperature. It works well for the narrow temperature range in the house. Outside is another matter. It is impossible to calibrate to the large temperature range outdoors. I would take the out door temperatures with a grain of salt.
