New sails have a much tighter leach than old worn out one’s.
Could be that with the leach standing to windward more your pulling the kicker on the same as you used to and its over working the leach.
This being aft of the pivot point that is the centreboard is giving you more lee helm than your used to.
Try easing the kicker to see if it reduces or work the mainsheet more with the boat flat.
CP