Purple Aster dying
It looks as though these Asters have a severe infestation of Chrysanthemum Lace Bug. They feed on mum relatives, like Asters, and cause this type of stippling damage. At this point, the damage is so extensive there is no point in trying to control the insects, which have likely moved on anyway due to lack of any feeding potential left (or they were discovered and mostly eaten by predators). Cut the plants back entirely as they may not even bloom this year; hopefully they will re-sprout and still flower late, but if they don't, they still may come back nicely next spring. To prevent future outbreaks, simply monitor the leaf undersides for the insects starting around late spring and blast any seen off with a hard spray of water. If persistent, they can be sprayed with horticultural oil or insecticidal soap, but contact needs to be made with the insects to provide good control, so make sure all upper and lower plant surfaces are coated as thoroughly as possible. We would not recommend the stronger pesticides recommended on this page, though there is more life cycle information provided: https://content.ces.ncsu.edu/chrysanthemum-lace-bug
Because they overwinter in debris on the ground, removing any remaining Aster stems and leaves this winter would help to diminish their numbers at the start of next year.