This is something that I did that had some of the same results as you are experiencing. I tightened the screw on the cutter too tight which caused the blade to nick the plastic on my almost new cutter. Thinking it was a bad batch of blades, I kept changing them. When that didn't work I bought a new mat, which I needed anyway, but, still was having the problem. I finally looked closely at my cutter and found the nick on the plastic. It could have been there when I bought it, but I think I caused it from having the screw too tight.