My axiDraw A3 has the same issue, so far only while drawing circles. The speed is at 20%. The resulting line is jagged. The AxiDraw itself makes quite a noise while jagging, and seems to vibrate with it. I’m tempted to avoid drawing circles for now.
Could it be caused by a (very slightly) ‘wavy’ drawing surface? I’ve made a short video of it, and have some pictures of the results for reference if you should need it.