Can you re-raise this here
https://discuss.px4.io/ - I'll have a look there on Wednesday if you haven't already had an answer.
WHen you raise this, show you connections using a diagram. I think it like this:
Mac <---- wifi ----> companion (ubuntu) <---- usb ----> PX4?
Any reason you are using USB for the connection? What is the companion computer? If it is an RPi you can do this
https://docs.px4.io/main/en/companion_computer/pixhawk_rpi.html