You say you saw sparks in the motors? Spinning freely and smoothly is not a conclusive indicator of the electrical condition. You may have one or more poles with an open circuit in the field coil and/or shorted windings. In a 12 pole multi phase motor it may still run however less efficiently. I would expect to see a CSC error reported if there is an open circuit (increases resistance on one or more phases) shorted turns may go unnoticed however and could lead to a later failure. I would disassemble the motors and check for signs of dmamge to the windings. They will be obviouslybdiscoloured if the temperature rating of the insulation has been exceeded.This would have been good to know (always learning) in this case the standard CSC would have been crucial.
Left stick all the way down. Same as what I tried when it was on the ground.
Coming from a P3P I did not know the Phantom 4 Pro CSC command is left stick down to the center and RTH button. Definitely feel foolish for not knowing this, and some how overlooking it in the settings.
Anyone have thoughts on overloaded motors? I did not receive any error messages, and the motors seem to be physically fine, bearings spin smooth and evenly.