Try using the steering wheel paddles to downshift before accelerating just to see if that makes a difference. You don't have to move the shifter out of D, just use the left paddle. It will go back to auto mode after a few seconds.
Could be the throttle body. If you can reproduce it then you need to get the tech or service advisor to ride with you and show them. Alternatively you can try a different Edge and see if it does the same thing.