No device found on ttyACM1 - even in bootloader mode

Hi,

I can't upload sketches to my Arduino Nano 33 BLE anymore. I already tried this: Arduino Nano BLE 33 - serial port down (Bootloop?) - #2 by pert to no success:

❯ arduino-cli upload --port /dev/ttyACM1 --fqbn arduino:mbed_nano:nano33ble --input-dir build
No device found on ttyACM1
Error during Upload: Failed uploading: uploading error: exit status 1

This is after putting the Arduino into bootloader mode using the technique described above. Yes, the orange LED is pulsating and I can see the Arduino in the board list:

❯ arduino-cli board list                                                                     
Port         Protocol Type              Board Name          FQBN                        Core             
/dev/ttyACM0 serial   Unknown                                                          
/dev/ttyACM1 serial   Serial Port (USB) Arduino Nano 33 BLE arduino:mbed_nano:nano33ble arduino:mbed_nano

Yet the upload doesn't work, failing with the error above. Is there anything else I can try? I did try with another Arduino BLE 33, which works perfectly fine.

Thank you!

Edit: It seems I can flash it, but only when starting the upload to ttyACM0 and then with good timing set it into bootloader mode. That's not really great. The other Arduino Nano 33 still works as expected.