Hi @dr_stony,
Most likely this is a powering issue, although it could also conceivably be a tether strain issue if the tether is pulled hard by the vehicle, or could be caused by strong electrical noise disrupting the signal through the tether.
I believe on x-box controllers these register as axes rather than buttons, and currently can’t be assigned button functionalities. The equivalent buttons on playstation (dualshock) controllers do register as buttons, and I’m not sure what happens for other controller types.
If this is an important feature for you you’re welcome to submit a GitHub issue, but there’s no guarantee of when the QGroundControl developers will have time to look into it and implement a fix.