Hi, I've never seen that before. Did you buy the bag new or pre used? If the latter, maybe a former owner used something that made the edge coating like this?
It's strange it's just the edge coating and not on the leather. Have you tried asking in one of the other forums, Hermès and
Coach, for example? I know there are some there who are very experienced with treating leather, maybe they can help. Also, I think there's a whole forum dedicated to these kinds of issues. Found it:
Find information on leather and general handbag care in this forum
forum.purseblog.com
Good luck, I understand this must be frustrating, hope someone more experienced than me can help!