Ran autotune on a S900 hex, and completed without any issue. Next, planned a 6 min map mission with 4 legs, at 100m Alt. Mission runs and returns to home point, rig descends from 100m to 50m, beeps, and stops descending. Same results at the finish on two additional flights.
And I pulled the params from another identical rig, THEN ran accel/compass calibration, THEN ran autotune, THEN ran the mapping missions. And halts at 50m. Not sure if autotune adds that into the mix or what.
And it could be the nut holding the steering wheel.