Can you find the section of Gcode that produces the problem? Find out if its written the way you would hand code it for camsoft. Then you know if its a control problem or a CAM software problem. If your control has generally been working on arcs, I'd strongly suspect the CAM software first.
FWIW, I was making a part with Mastercam developed Gcode just last month that did this in one spot. i ended up hand editing the offending line of Gcode.
Karl