SAMD21 enumerating on MacOS, not on Linux

[romix123]

I have built a MIDI controller based on a Samd21 (Adafruit qt-py bootloader). It enumerates correctly on MacOS and notes, CC and PC messages come through correctly.
The board does not work on linux hosts ((monome norns, rsta/minisynth, bare linux). The test code on the main lib page “
execute aseqdump -l; the output will be something similar to

Port Client name Port name
0:0 System Timer
0:1 System Announce
14:0 Midi Through Midi Through Port-0
20:0 Arduino Micro Arduino Micro MIDI 1”

only produces the 2 system lines.
What’s up?