Thanks very much for your suggestions!
I removed the RX listening mode and tried the LMIC_ENABLE_arbitrary_clock_error flag, but to no avail. Going through the different SFs for the JOIN request via LMIC_setDrTxpow did not seem to work, either. The TTN Console always reported SF7 for the first JOIN message it received.
Unfortunately, I do not have access to my own gateway, so I cannot see if the network always transmits a JOIN_ACCEPT message, and via which gateway of 4-5 I am in range of.
I’m also having trouble with two additional aspects. Maybe someone here can give me a link to additional resources?
- Enable LMIC interrups on Adafruit Feather M0
- I did not manage to get debug output to work on the serial monitor with my feather M0. This seems to be a known problem.