It could be residual fat from the leather rising to the top. This happens to a few of my Hermes bags, I’ve never seen it on a Chanel bag. You may be able to find a thread on it in the Hermes forum. As per the suggestions from that forum I have either VERY gently applied some heat via a hair dryer and rubbed off the fat spot with a Q-tip or wet the Q-tip in hot water and gently rubbed the spot off. It always works for me but other spots may appear. I think it’s normal and the result of temperature fluctuations.