Your issue can be a number of things causing the cutter not to cut properly.
Dull blade or broken blade tip. I have seen a plotter blade last over a year and I have seen one fail in 3 days. I have had really good luck with the Clean Cut blades.
http://cleancutblade.mybigcommerce.com/graphtec-cb09u-25-m/
Cut strip. Is there a groove in it? Are there nicks in it? If your unsure replace it.
Cutter head. Is the cutter head tight on the guide bar?
As far as settings- I run my Graphtec cutter, when cutting tint on 35 speed and 15 to 16 pressure, on a new blade. The pressure will vary on the manufacturer of your film.
Once the blade depth is set correctly on a blade you should never need to change it. When the blade gets dull, up the pressure, don't change the depth. .
Good luck.