Sometime when i start to look my application at ttn console, it shows that there are some uplink messages and these messages are sucessfully forward. But it did’t show the vaild payload as below:
Another, different, reason is that sometimes LoRaWAN connection housekeeping messages are exchanged, these have a port value of 0. On the MQTT stream they can appear with empty payloads. So, on the application side you probably need some code to ignore these.