Mold/mildew on leather seats, How to remove and prevent from happening again

My dad has a 2018 F150 King Ranch that sits for long periods of time (in a pole barn, concrete floor, currently non-heated, but very dry) and it has what appears to be mold or mildew forming on the leather seats. It’s mostly on the back side of the seats and it looks like you powdered them. There is no musty/mold smell in the truck, still smells brand new, so I’m not positive it is mold, but I can’t think of anything else it could be. What could have caused this? Could it be residue from something the dealer applied to the seats? What would be the best way to remove this? Will a leather cleaner or a cleaner conditioner combo product be sufficient? Will using a cleaner/conditioner prevent this from happening again?