It seem that one album got different genres
The Very Best of Fleetwood Mac Front Cover 2002 Classic Rock
The Very Best of Fleetwood Mac Front Cover 2002 Rock
The Very Best of Fleetwood Mac Front Cover 2002 Rock
The Very Best of Fleetwood Mac Front Cover 2002 Rock
The Very Best of Fleetwood Mac Front Cover 2002 Classic Rock
The Very Best of Fleetwood Mac Front Cover 2002 Rock
Genres double named
By default because they are so subjective genres are only added if missing, so I guess that some of your songs already had a genre and some did not, please check your settings.