Hmmm… I’m positive I’ve changed tags (misspelling, etc) and then did a refresh and the new tags are updated properly. That was supposed to be one of the improvements with the new music system -the elimination of the Plex dance. I think you might have to refresh at the artist level in most cases, but I’m not sure about that.
I think a “re-fresh” of the metadata is the key, rescanning probably does as @anon18523487 suggested, and the tags are not read.
