CJV150 plotter inconsistent

Hey, I have a CJV150 and I mostly make dirt bike graphics. I started making graphics in 2019 so I'm still a bit of a newb, but I cannot get this thing to cut at a consistent depth. I was cutting some kits the other day and I had cut about 5-6 sheets and it was cutting pretty consistent, threw in another sheet to cut and it was hammering right through the backing paper. Nothing changed. Same material, same pressure, same heat. This is an issue I've been battling ever since I have started. Even on the same sheet it will cut through the backing paper randomly. Any suggestions? Or do I just need a standalone plotter, like Graphtec to be more consistent? I am using 21 mil material and a 30* blade.