I have very similar results with the M0 version: Adafruit LoRa Feather -> Gateway
If both the M0 and 32U4 platforms have the same or similar issues, then i suspect the LMIC library might be to dependent on the Atmega328P. Has anybody got it working on an non Atmega328P processor?
I have some issues with the M0 and outputting to serial port. This makes it very hard to debug. I have spent many hours trying to figure it out, but no luck.