The sharp corner shown with the arrows (down and to the left) is produced when the machinery is a little loose, reverse direction and the machinery ‘takes-up’ the slack. The soft predicted corner (opposite - arrows down and to the right) is generated as the engraver is continuing in one direction.
If you have a machined flat on a shaft and the set screw is slightly loose the motor will move without moving the gear causing symptoms similar to what you’re seeing.
Please check set screws and other possible loose components and report back.