You error message indicates that the ACM module is built in to the kernel:
“rmmod cdc_acm” returns “ERROR: Module cdc_acm is builtin”
If the device does not show up in lsusb, then it then it will not show up as /dev/ttyACM*.
If present, the device should show up with 0483:5740 STMicroelectronics STM32F407
My guess is that you have a bad connection between the device and the usb plug. If this is one of the new generation FOCBOX, the wall of the case is slightly thicker, which may cause the microusb plug to have connection issues. You can try using a different microusb cable (the Jetson TX2 programming cable seems to work ok most of the time) to see if that’s the issue.