Yes, If you set ENABLE_UPLINK_CHANNELS=0-7,The LoRa Server will send block of maccommands to disable all channels first. And second, LoRa Server send block of maccommands to enable the channels that your select, channels 0-7.
So make sure your sub-band 1 which is channels:0-7. And then make sure your flag ENABLE_UPLINK_CHANNELS are correct. If correct the LoRa server should result in something like this in the logs:
INFO disabling all channels
INFO enabling channel block first_channel=0 last_channel=7
And I’m sorry, my english is not good, I worry about are not very good in communicating with you, So this is for your reference only.