Some things for you to try if you are still having issues.
1. Check cutting strip/pad. If it has cuts and scratches on it you can get problems similar to what you have. This will probably be damaged if you have cut on a high pressure with a new blade. When you do a test cut you should be able to easily weed the circle and the square from each other while only leaving a slight tracing in the backing
paper.
2. Blade holder has a bearing in it that may not be allowing the blade to turn freely, this can cause the blade to skip along the material - remove the end cap and clean the bearing, light spray with WD40 or similar.
3. If the tip of the blade is missing or chipped you will not get smooth cutting.
4. Make sure the pen force slider on the front is set to "0"
5. You should only have a small amount of blade extending from the blade holder approx 1/2mm to 1mm. Also if not enough blade is out, the blade hold end cap can bounce around on the material.
6. Offset for the type of blade you are using will need to be correct, otherwise you will get rounded/torn corners. Standard blade should be 0.250.
regards
Brett