Anne’s comment re halyard tension is correct.
Our Facnor furler was also stiff but easing the halyard a little made all the difference. I think too often sailors tension the halyard and then just leave it for a season but that means high tension all the time which means the sail can stretch more and more as well as furling being difficult. We put a ring of white tape around the halyard on the mast and got to know where it should be when furling and unfurling as well as for different wind/sail settings.
The membership association for owners of Dufour Yachts