‘Song’ sync does ignore categories and favorites
The ‘Song’ sync does ignore categories, as it is foreseen to sync songs with band mates and every band mate can have other categories. If we would add all categories of all other users, you would have probably too many of them. The other problem is the content of the categories. How could you get the items of new categories? There is just the selected item in the song. And what should happen if your band mate does have the same category, but more or other entries in his categories? Because of these unsolved questions, we decided to ignore categories in the ‘Song’ sync.
Imagine an “I can play this song” category. If we would sync the categories, your band mate would get it tagged “I can play this song”, even if he can’t play the song.
The same applies to favorites. Would you expect that your songs are tagged as favorite, just because your band mate loves this song? Favorites are in our opinion also personal settings and not meant to be shared.
The ‘smartChord’ sync is foreseen to sync the own devices and it also syncs the categories and favorites: https://youtu.be/OSqfxE42kUs