You’ll need to determine what the downlink is. Like if it’s an AU915 “Initial ADR” in which TTN tells you what channels to use, or if it’s some other MAC command in which TTN tells your device to adjust its settings as it’s using a bad data rate, then you may not want to ignore that. It may also just be a confirmation (ACK) for a confirmed uplink.
To decipher the downlink see LMIC Library Always Does Unwanted Downlink.