@Eric-Katzfey : I'm not running any custom software other than voxl-vision-hub.
If I stop and disable voxl-vision-hub, the "set_position_target_local_ned: coordinate frame 0 unsupported" error goes away !
With this I am able to complete calibration (compass and IMU) successfully in GQC, BUT drone fails to arm in Position mode even though QGC shows "Ready to Fly" and all Sensor status show as "normal".
Checking VIO in VOXL Portal shows correct operation of VIO: VIO plot follows drone motion, which seems to indicate that VIO is working fine, but
QGC shows "Yaw estimate error" , and "--" as altitude estimate, which prevent the drone from arming in Position mode.
Then I re-enable and restart voxl-vision-hub.
Now GQC receives altitude estimates and I'm able to arm the drone in position mode !
So the trick seems to be to disable/stop voxl-vision-hub, calibrate IMU if needed, and enable/restart voxl-vision-hub, to be able to arm in Position mode.
Seems odd but I'll take it ! Let me know if you have any comments or suggestions. Thanks.