I have a major mildew problem. I didn't notice in the bag before I washed it but you can see spots in the seller's pictures. I think washing it made it a lot worse. The entire flap is covered inside and out with mold spots. It looks like it goes all the way through. The flap is very stiff and crunchy. I rewashed the bag with oxyclean and put it in the sun. I believe the mold is probably dead but the spots and crunchiness are still there. I put one coat of Leather Honey on it because it says that it resists mildew but the spots didn't absorb the conditioner. I'm sanding the suede of the inside flap in an attempt to soften it. What else can I do? The spots appear to be a little recessed on the surface of the bag.
I had an old penny that had the beginnings of a mold issue when I got it. I didn't realize it either at first. I let the bag completely dry out then used Blackrocks on the theory that it would both clean the leather and provide waterproofing. I think I may have read somewhere that Carnauba wax would help with inhibiting mold growth. I then put the bag in a cool, dry room for a couple months stuffed with a clean, dry cloth. The mold doesn't seem to be regrowing. I'll be interested to see what others have done.