I once experienced that dark glazing of my Soho bag left some dark stains on my white shirt. It was a hot sunny day. The stains looked a bit similar than those on your bag. I could wash them away though and the shirt was not ruined.I personally love and continue to buy Gucci but had more than a few incidents. I had an older Gucci bag that I got and the blue dye from the leather trimming started leaking into the white canvas. It was a very special piece but I brought it back after like 7 years later and they gave me a refund. I barely used that piece. I then bought the Gucci Ophidia mini bag. The screw that holds the strap onto the bag fell off twice. I screwed it back the first time but it fell out again after I was shaking my leg and the bag was on it. They gave me a refund again. Lastly, I saw a “new” pair of gloves in the store with the stitiching already popped. I would never stop buying Gucci though since customer service has been superb. I don’t have any problems with my RTW pieces.
Gucci quality is excellent but what I’ve experienced the glazing is the weakest part of the bag as in a few cases I’ve noticed it can melt/ stain or crack.