I have one user who is missing some appointments on his iPad that are on the iPhone. After trying to resync the devices, remove the calendars, etc., I eventually removed his account from the mobile server and used dsapp to remove his info as well. Then added back his account to the server and mobile devices. But he is still missing SOME appointments on his iPad that he has on his iPhone. They are both at the same iOS (9.3.1). I'm looking for another iPad I can add this user's account and see if the missing appointments show up, but thought I'd throw this out in case someone else has seen this.