Were the lines all colourful before you hit go? If any item is grey some part of it is outside the limits of the machine and will not work.
This is a different design - but see how the pieces look like they’re even, but one on the right is actually a single space lower than the one on the left and is therefore outside the cut area so won’t cut.
When you have selected an item a big grey bar appears around - that’s your out-of-bounds.
