For general information here is their video.
If the hole spacing is changing, either the adjustment screw is not tight enough, or there is another loose part in the advance mechanism flopping around. If the adjustment is slipping, you should be able to see it move while you are using it. Don't turn backwards at any point during operation. Always crank clockwise.
Make sure your strap width adjustment is not binding against the strap, though I doubt that could change the feed distance as the punch tube is pulling the strap through. Worthwhile checking though.
Another thought could be the tube is being lifted out of the strap while it is still advancing.
Hope this is of some help to you.
Tom