As this was the only result I could find about Onoclea sensibilis fern ring I wanted to add a reference to a wild fern ring I found of the species. This was found in the fall, 2022, in WV during a hike. I do not know the age of the patch of ferns.
This response, I hope, should act as an answer to the question for documentation of a sensibilis fern fairy ring.
As reference and showing ownership of copyright, I originally posted this image on instagram here: <
![Onoclea sensibilis fern fairy ring](