Solved! Go to Solution.
Spotify woks only with Ford Sync 1.1 + Applink devices.
I can confirm this because my old car (Ford B-MAX) had the Sync 1.1 with Applink and spotify worked always well.
Now I have a new C-MAX with Sync2 (no applink features are available), and I can use Spotify only with the standard BT streaming.
Note that with the Sync 1.1 with applink yor car will display all the Spotify functions (Playlist, Album, Radio...), with Sync2 you will not have this features.