Stars are needed to unlock chapters? That must be since the Spring update. Before, only a certain amount of missions had to be completed.
You can try to report this bug to Gameloft, but don't expect them to reply. I can't help you, I'm afraid.
Same thing happening to me, restarts to 89 stars and wont unlock.
mine too!! i'm struck at 87 stars. if anyone find any solution for this pls post in this thread.