I've seen this on one of my Lavender plants once...now one of my BES has a mutation as well. Just one single stem is flattened and 2 leaves grew into each other...looks cordate rather than lanceolate and the flower bud looks like 2 melded into one another.

I had frog hopper spittle bug larvae up the wazoo this year but only noticed some leaf curl/distortion on some of the BES and Ratibida. I don't think they caused this do you? What is it?