Could be arrow spine. Could be bow-hand torque. One thing often overlooked is cam lean, or in this case possibly idler wheel lean. If the cams aren't square with the limbs and riser the string is going to oscillate sideways on the shot, basically driving the nock sideways as the string travels foreward. If this is the case then try twisting up one side of the yoke to square the idler wheel. If you have sever cam-lean (bottom limb then you're stuck with what you got---thus, one of the pitfalls of the "blessed" solo cam.