G'day and welcome to TBN when you say it curs the knot is it cutting through the knot or is it not tying the knot , is it a clean cur or a ragged cut sometimes a blunt knife will give problems like that i don't think it is out of time as you would more than likely have prob with both the knotters, is the twine tension where it comes out of the box the same for both ? just a few things to look at