[JanneT]

Are you absolutely sure that "Giacomo Puccini" isn't in any tag of any music file? In ARTISTS, ALBUMARTISTS (note the "s") tags perhaps? That is the most obvious reason. Since it works when you remove them, then it is unlikely to be a COMPOSER or PERFORMER tag, but it is worth double checking those too.

Yes, you were right! I finally found the problematic album. Then I realized what a mess my tags were. Lots of conflicting and redundant ALBUMARTIST, ALBUM ARTIST, ARTIST and ARTISTS tags. But at least I know how it happened. I have to be careful with Picard! I spent this morning to clean it up, and the scans perform as expected now.

Thanks!