Never heard of this one before, but it looks like a stage before root rot, the moss is staying wet too long, not allowing the roots to breathe. I would suggest a repotting in a open bark mix. Remove the moss gently not breaking off any roots, you can do this by putting the plant in water and then gently shaking the plant side to side, most moss will come off, the remaining can be removed by hand or tweezers. Then spray with hydrogen peroxide or a fungicide and repot. Don't water till you see new roots forming, just mist the plant everyday and keep it in a bright shaded spot. Hope this helps.