This does not look like symptoms of Aster Yellows, but perhaps more importantly, this does not appear to be a Coneflower (Echinacea). It resembles Stokesia (Stokes Aster), though it's hard to be certain from the images provided. Various factors can cause "bud blast" (the failure of flower buds to open), including fungal infection and feeding damage by thrips. Trimming off the affected flower stems in those cases will reduce the risk of a recurring outbreak.

Miri