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Mine was doing the same. I signed out completely out of iCloud.

settings>iCloud. scroll to bottom and sign out

Rebooted the phone and then logged back in.

No problems since.
 
Ok I tried the sign out, but didn't reboot. I'll give it a go.
 
good luck.

If you have any other iDevices with the same iCloud account, you may need to do the same.....
 
every time I open iTunes it asks me to login to iCloud twice. Every time. Twice.
 
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