SONOFF SNZB-04 is one of the most difficult to troubleshoot Zigbee devices.
It operates in a 'deep sleep' mode all the time, the only exception is when it is paired to the hub, when the contact state changes or when the battery level is reported (battery reporting is problematic too). It is not possible to ping it or to know in any other way if it is online to the hub or not. A few white hairs on my head are because of this sensor..
My advice will be for critical applications (like monitoring salt levels..) to use another contact sensor.
You can still use the SNZB-04 for less important applications, preferably closer to the hub.
