Why report when there is no “really” change from the sensors? This will only drain your battery.
The Xiaomi sensors (I use 9 temp/hum sensors of them) reports only by increase/decrease values. This means in some rooms I have sometimes a reporting of every 2-3 hours .
You can also try to breathe your sensor. Mine then responds after a few seconds.
Maybe the Sonoff reacting the same way like the Xiaomi sensors?