Might be a missing steps issue, if you haven't done any other setup? The machine has been told to accelerate or move at speeds beyond its capabilities and the stepper motors can't keep up - could be why it moves correctly in air but not when cutting which puts more load on. Try halving the max speed for each axis and halving the acceleration, and see if that helps. If it does, then you can start winding things up a bit to find the limits.