Pure coincidence, but I just discovered in my library multiple instances of artist duplication – exactly as DrTone described above. Each respective duplicate indicates a different number of albums but directs to the same artist page with an incomplete roster of albums. None of the duplicates can be merged.
A full or at least partial solution I found through trial and error was to select one or all albums under an affected artist, then instruct Roon to re-identify those albums. In most cases, Roon would spin for a few moments, re-populate all of the correct albums on the artist page, and remove the duplicate artist
AJ