I just had this problem a week ago! I changed the blade and it seemed to have a nick. I took it off and put it back on to make sure I hadn't put it on incorrectly. I tried another cutting mat. I changed the blade and it still seemed to be jumping. I pulled out another rotary cutter and it worked fine! I tried yet another blade and now it's fine. I guess there were just a few bad blades in the pack. Of course, I bought them a long time ago with a coupon so I don't have a receipt, but lesson learned.