It sounds like clematis leaf spot….not an uncommon problem, especially in a rainy year like this one. I’d suggest removing the spotted leaves.  Also, never spray water your clematis…wetting the leaves encourages all kinds of fungal disorders.  If removing the leaves doesn’t solve the problem, then applying a fungicide might be in order.  Here’s a link that describes the various diseases that can attack clematis: https://extension.psu.edu/clematis-diseases