@williangalvani has recommended trying the latest ArduSub beta firmware because it’s very recently been updated, and he hasn’t come across the compass drift issue on that version. It should be possible to update to from the Companion web interface System page, or via QGC if you directly connect your Pixhawk to the topside computer, or from the Autopilot/Firmware tab if you’re using the Companion Beta (select “Sub” for the vehicle, wait for the available firmwares to load, then Beta is the bottom option in the dropdown).
