I still believe that a chemical reaction is unlikely to be the problem. I'm proceeding assuming this is an exception.
Can you post a picture of the color before and after recycling? Does the recycling involve neutralizing it with caustic soda?
I'm assuming you talked to the manufacturer of...
My first suspect is still the cloth.
If it isn't, a little more info would help.
What was the reason for stepping up the PAA concentration?
What temperature do you run your CIP process at?
What other acids/acidic cleaners do you use?
Does the water come into the brewery from copper...