Maybe you already tried this but how about parking the boat sideways to the wind (room permitting), then uphaul the halyard ring and hold it up while you rotate the mast hook upwind? That might get the ring off the hook if you keep the ring pulled up high as you rotate the mast, then release it.

I have trouble sometimes getting my Prindle mast hook to let go of my halyard ring unless I turn the boat, bows across the wind about 45-90 degrees. Bows dead into the wind it almost never comes free.