It might be heat, I have had the same problem this year. No fungus issues, but definitely heat, and my leaves also look well. Perhaps others will give you their views on this.

I don't think heat is the problem. I live in Md. and we've had a pretty mild summer.

I don't think it's the heat, I think it's too many cloudy/rainy days? We've had a lot of rain this summer and our extremely vigorous, healthy patch of A. tuberosa put out a lot of flowers but the resulting pods are small and withering....no viable seeds. Two other species in the area, A. amplexicaulis and A. exaltata growing wild in nearby wet woods, have numerous, beautifully viable seed pods. This difference (possibly in my non-expert opinion) is maybe due to the fact that A. tuberosa and A. syriaca both prefer to grow in full sun...the other 2 species are woodland species so maybe they haven't suffered in the wet weather but the others require a bit more sun to produce viable pods?