Are there many like this?
It's not clear who/what is the culprit, as this is not common, but it's possible it is a stem borer, which would be the larval stage of a moth.
When you straighten the stem, any sign of a small bore hole, or did you notice any sawdust-like frass coming out of the stalk?
Try slicing the stems and see if you find an insect.
It is possible it is environmental in origin as well, but given you are seeing it yearly, we'd lean towards the borer.
We don't suggest treatment other than to look for the borer and squish it, clean up well in the fall, and keep tall weedy areas weeded or short as that is where eggs are laid in late summer and is their first food source before they move on and eat your coneflowers.