The lift motors started because the aircraft was badly out of attitude

What ArduPilot says:

• Angle assist r=N p=N

Assistance is the lift motors switching on by themselves in a fixed-wing mode. Here two things held for longer than Q_ASSIST_DELAY: the aircraft was more than 5° outside its limits (ROLL_LIMIT_DEG, PTCH_LIM_MAX_DEG, PTCH_LIM_MIN_DEG), and its roll or pitch was at least Q_ASSIST_ANGLE (30° by default) away from what the autopilot wanted. r and p are the roll and pitch in degrees at that moment. The lift motors now pull it back level. It needs Q_ASSIST_SPEED above 0.

What to do, most likely first

1. A stall or the start of a spin: the aircraft was too slow for the turn or climb it was in.

   CheckIn the log, the airspeed in the seconds before the message, against AIRSPEED_MIN.

   FixKeep AIRSPEED_MIN well above the stall speed at your weight, and Q_ASSIST_SPEED set, so that the lift motors come in before the wing lets go.

2. A control surface stopped working: a servo, a linkage or a hinge.

   CheckAfter landing move every surface from the transmitter in MANUAL and watch for one that lags or does not move.

   FixRepair it before the next flight.

3. Strong turbulence, or a fixed-wing tune too weak to hold the attitude.

   CheckIn the log, compare wanted and actual roll and pitch in ordinary flight.

   FixTune the fixed-wing controllers (AUTOTUNE mode) in calm air.

Parameters to look at