I have tried multiple braids over the years and it just seems on occasion, that I get these random break offs. It doesn't mater if it's new or old line. My knots and guides are fine.
It took me years to come to an odd conclusion..... it's me, not the line. When I cast, I tend to whip cast it sometimes. The force of the whipping action gets transmitted to the knot, causing the break. Also, i find myself asleep at the wheel on occasion and I set the hook on slack line. Doing this repeatedly seems to weaken the line in general. Braid is great but it does have its limitations based on how I fish.