Alexander, I just gort it working. I'll have to play to see how reproducible this is, but this is what I am seeing ...
I insert the device. It is configured on ttyACM0, but does not work. I remove the device and replug it. It still does not work, BUT I now have ttyACM0 and ttyACM1. NM is trying to use ttyACM0, but the device has apparently now been moved to ttyACM1. I remove ttyACM0 and symlink it to ttyACM1, and the modem starts working.
Alexander, I just gort it working. I'll have to play to see how reproducible this is, but this is what I am seeing ...
I insert the device. It is configured on ttyACM0, but does not work. I remove the device and replug it. It still does not work, BUT I now have ttyACM0 and ttyACM1. NM is trying to use ttyACM0, but the device has apparently now been moved to ttyACM1. I remove ttyACM0 and symlink it to ttyACM1, and the modem starts working.
Got a clue?