Same thing happened to mine. Took it in to get it fixed under warranty and they had to replace the whole shift knob. Took a few days because apparently the part wasn't available in the States and they had to get one shipped over.
It’s snapped in half as you can see the fatigue crack in the middle on both sides you look carefully. And when I put it back into place it’s doesnt ‘click’ in to place. Guess it’ll be a warranty issue when I take the car in for its MOT/service.
My car is out of warranty and the half red ring has snapped off, I don’t have the other half of it so unable to glue back in. Is there anywhere to buy just the ring or will I have to replace the whole knob?