Addeing Favorites and songs to Favorites

I just got my Sandisk fuze back from repair. I don’t remember or if it’s the player.

I can’t add songs to my favorites list, when I do it syncs, you see the % complete and even says you may disconnect sync complete. But there are no new songs. So I tryed to add a second favorites and the same exact thing happens. The only way to add is to delete the entire favorites list then re-add it with the new song.