Still have unanswered questions. Is it getting stuck in the same place? Are you cutting into the mat? If it is getting stuck in the same place, adjust the file. You can easily turn sharp corners into rounded edges in the file. The cut will still look like a corner, but the blade will have an easier time. I have a friend who designs files who does this on all of her files and they cut like butter - never a problem.
Have you cut that particular leather successfully or is this a new material. It could be the leather - they all do not cut well. Try the file on something else to be sure there are no glitches with the file.
Try reversing the leather and cutting on the other side. Also try (after you have checked everything else) flipping the file. Sometimes that helps - there is no reason for it, but I have seen it work when nothing else does.
Still lots of questions.......