Not all ibooks syncing between ipad and iphone

I am trying to sync about 1500 ibooks from my ipad mini to my iphone 6 but it will only sync about 1400. I transferred all purchases from my mini to itunes and then synced my iphone but certain ibooks will appear then disappear or will only open to a blank white screen then disappear. Not sure what happen or how to fix this. All started happening after ios8.