I fixed following the reset parameters tip on this page:
https://discuss.bluerobotics.com/t/ardusub-4-1-0-thrusters-not-answering-joystick-commands/12720/10
I’m using 4.1.0 beta (as I need DVL functionality), QGroundControl 4.2.3, and companion 0.0.31.
Waiting to go to the field to test DVL poshold.