This is the 2nd easy set pool we have had with same issue. The top ring gets a sticky feel to it and some black dots that turn crusty. After carefully maintaining the pool for winter, when we unpacked it, the entire top ring looks black and crusty. What would cause this?
It is probably mold or black algae. This can usually be avoided with proper cleaning and thorough drying before storing it for the winter. Damp/wet is your enemy for long term storage.