@arjanvanb I am having exactly the same problem with a Dragino LPS8 for the AU-band. The LoRa device sends the downlink in the 917 MHz range channels, and the downlink information is received correctly in the TTN console. but the gateway answers on 868.525 MHz, being the EU RX2 frequency. Or at least, I think the gateway doesn’t even transmit this message because it is not suited for the 868 MHz band, but the TTN backend shows that it selects this frequency.
In the console, the frequency plan for this gateway is defined as Australia 915MHz, so everything seems fine. Do you (or anyone else) have a clue why the TTN server persists in sending a message in RX2 on 869.525 MHz?