Can you post a picture? One of the frog, the blister, and the enclosure? What is your humidity and temp? What do you use for bedding? (I've heard of moss growing some undesirable things...)
I'm new to WTFs so I can only give you really basic advice. Just what you're describing sounds kind of like some sort of bacterial thing (I dont know, it's 6am and I've been working with bacteria all day, so maybe I'm just fixated on that)
The more info you can give about the frog's food, enclosure, and whatever other information you can think of the quicker someone who knows more about WTFs can help you.
Best of luck figuring out what's going on
