First thatn anything check that you have the correct blade selected in your cut conditions, if your using the blue nob blade holder then make sure you see 09U on the display as part of your cutting conditions. once you make sure of this double check the combination of blade length and cutting force, only extend the blade the thickness of the material layer only, then perform test cuts increasing the cut pressure until you able to weed out the test cut.
If you still have the problem then it may be your blade holder- the blade is no longer swiveling w/ in it. to isolate the plotter from the tool take your Graphtec pen, a paper, change the plotter to PEN mode force of 12 send the same job over, if the plot comes out the same then call tech support, if not then replace your blade holder.