Apparently some firmware changed the emergency Phantom 3 Emergency Engine Shutoff procedure, but the DjI manual has not been updated to show this new procedure.  The manual still shows the CSC maneuver to shut off the motors, but it has been changed to a left stick (throttle) down and press the Return To Home button to immediately shut off the motors.

Hi there. Thank you for reaching out. I will forward this to the designated team for their attention. Thank you for your kind and understanding.

Most DJI User Manuals never get updated to reflect changes in firmware updates.  Just saying.

I can confirm that the motors on my Phantom 3 Advanced will not stop quickly no matter what I do with the controller sticks and the RTH button. ANY movement of either stick downwards and towards either the right or left corner results in the motors speeding up for about five seconds and then stopping.

The quickest and safest way to stop the motors is using just the left stick pulled straight back. This stops the motors after about two seconds with no speeding up.