Unfortunately, this had the really bad side-effect of dropping the "host" that was providing just "cluster01" service. All attached volumes continued to work fine. However, it became impossible to launch new instances with these volumes, terminate (properly) instances with these volumes, or delete these older volumes.
The fix (once you understand the problem) is very straightforward:
cinder-manage volume update-host --currenthost cluster01 --newhost cluster01@ceph
NOTE: Don't do this unless these are really the same services. Presumably safe if you have a single cinder backend and are prepping for multi-backend.