Answer for syncing Genesis

Great question.  I ran into this same question.  It turn out that adding Genesis shows or movies to your favorites is completely separate from adding them to your library.
There is no way that I’m aware of to sync your favorites across multiple devices because favorites are not a part of your library.
But, after you see what you can do by adding Genesis shows and movies to your library, why would you event want to use the favorites feature?  I only open the Genesis add-on when I’m looking for something new.  When I want to watch a show that I’m already watching, I just go to my TV Show library and it’s there.