The reason of fail to join KPN is that our end node use RX2DR=3 for join. this is the default setting for TTN and many LoRaWAN servers.

The KPN use RX2DR=0 for Join, when KPN sends a Join Accept, due to RX2DR different, the end node can not receive the Join Accept message from KPN so keep joining.

Some of End Nodes already support the change on RX2DR for OTAA join, in this case, use need to write AT+RX2DR=0. Please contact Dragino support for more info if the product doesn't support it.