I added an ID and deleted it, no maverick now.
The misplaced mavericks seem to crop up around changes in taxonomy. Adding and deleting an ID has fixed it all the ones I’ve encountered, which is at least dozens. Just be aware that deleting an ID unfollows and unreviews the observation.
previously:
https://forum.inaturalist.org/t/what-is-a-maverick-id/49044