Challenges keep disappearing on Candy Crush Saga

I play Candy Crush Saga on both my iphone and on my Samsung tablet. For about the last two weeks, every time I have a new challenge (sometimes more than one), after less than a day the challenge completely disappears from my game on the iphone even though it is not close to the expiration time. I know the challenge still exists, because this does not happen at all on my tablet. For instance yesterday, the Diamond Path challenge showed up on my iphone and still had about 5 or 6 days left on the time. This morning, the challenge was gone and there are no challenges on my phone. On my tablet, it still shows the Diamond Path challenge (with 111+ hours remaining) and the Dexter's Delight and Universal Love challenges are there. This has happened with EVERY challenge recently on my iphone. I have completely closed the game, have restarted the phone several times, etc. and nothing makes the challenge(s) reappear. Why is this happening and how can it be fixed? Thanks.