There is not a specific patern on the side where the problem occurs and it is not in all the reels. Because it happens on either side of the reel, it would seem that when you manufactured this batch, some parts of both sides of your mother reels were over-stretched so, when you slit them down to the required width, you did not fully removed the over-stretched areas and that leaves a slack side. This would be why, when we use a reel that comes from the middle panels of the mother reels, there is no slack band present, but when we use a reel that comes from the side panels of your mother reel, this is when we experience the slack band issues.