Originally Posted by JustAbitCrazy

For me, when this happens, it's because the blade ran up onto the top of the plastic ruler a tiny bit. Some of my rulers have little slivers taken out of them along the top edge, or (especially) at the bottom corner, where you first start to cut. Some of the corners are a bit nipped there. Dulls that part of the blade immediately, and it will skip cutting in that spot with every revolution.