I had a normal flight in front, but the same problem occurs. The two changes were the second aircraft and the second FC.
X-UAV pixhawk2.4.8 ver4.0 20200801.param (16.8 KB)
Are you sure that the ailerons deflect in the right direction in FBWA mode ?
Docs: https://ardupilot.org/plane/docs/guide-four-channel-plane.html#servo-function-reversal
Servo 1 setting “4”
servo 2 setting “4” reverse settings are correct.
However, the left and right channels of the aileron are independently set. In my opinion, the tail motor doesn’t seem to turn off over time.
A link to the logfile would be helpful