There can be several factors that cause Coneflower blooms to be malformed or missing parts, but in this case Aster Yellows is not suspect based on the pictured symptoms. You can keep an eye on the plant of course, as an Aster Yellows infection will only progressively get worse and its symptoms more blatant due to the nature of that pathogen. Clip off any malformed flower heads in case mites are present to try to reduce their numbers. We agree this looks more like Coneflower Rosette Mite damage than anything else (outside of environmental stress perhaps); the linked page has more information about this mite and comparisons with typical Aster Yellows symptoms.

Miri

You're welcome!