They couldn't pinpoint exactly what, but guessed something spilled on them. It is interesting that they all looked the same but showed up at different times. I am going to pay attention more. Doing this also got me to realize I am getting a little sun fading and it prompted me to clean, condition, and protect using the Leather Solutions kit that was mailed to me when I bought the furniture. I am now going to set a reminder every 4 months to do so.