Feather M0 uplinks on two subbands?


I am using a Feather M0 (SAMD21) setup with Arduino MCCI LMIC LoRaWAN library. Using a MultiTech LNS and Chirpstack LNS, i see the board send uplinks on two different subbands. If i configure it to use SB2 and my gateway has two radios configured SB1 and SB2, the board will join on SB2 and will send uplinks on both SB2 and SB1. I would like to the board to only used one SubBand. Any ideas how I could setup the board to make it only stay on one SubBand?