Chops and Chop Serves have so much backspin that attacking will continue the ball's spin direction which would drag it down into the net. You need to return chops with a backspin stroke in order to counter the spin and lift it up over the net.
The ball trail, the backspin button and the screen edges will glow blue to remind you.
👍 TOP TIP
Players with a Mega Loop can attack chops and chop serves. This is because it generates enough lift to get the ball over the net. This also generates an extra boost on the loop as it now has extra topspin.