This is a common issue when the sensor has not transmitted data yet. In this scenario, a sensor was activated and is collecting data. However, it can only transmit the data, if there is a gateway close by. If that is not the case, the sensor will simply store the data locally and send it whenever it comes near a gateway. 

Please note that it is possible that some sensors in your fields do send data and others don't. The LoRaWAN network protocol has it's tricks and merits, which sometimes lead to behavior that seems unlikely. At the latest when the sensors are returned to Valenco, we will help you to get the data from the sensors. 

For any further questions, feel free to reach out to support@valenco.ch.