The problem is not the string but rather the angle of the string above the stationary post. On lever harps the string has to go from the tuning pin to the stationary post(with the notch in it) more or less in a straight line. If there are too many windings on the tuning pin, and the string above the stationary post angles in towards the wood neck, then it will pull the string out of the notch. You may have to unwind the string from the tuning pin, pull up the slack, and then wind it up again to put the string in a straighter line.