I did the same on my side. I rapidly checked the first 50 albums in my library with a review, and could not find ONE review with the reviewer name identified, whereas the name appears on Allmusic.
My library is however mostly composed of classical music. I do have however some old pop-rock-folk albums which I very rarely access. Surprisingly in those cases, the reviewer names are displayed at the bottom as you say.
The fact that the great majority of my classical albums exhibit this problem explain why I may have given the impression that this was a global issue. I realize that this is not the case for non classical-type albums.
But, IMHO again, I still see this Roon behavior as problematic.
Regards