icloud deactivated on iphone ramdomly

Hello,

on my iphone 4 iwht latest ios 7, icloud switch ramdomly off without any action from my side.

I don't have any contact name (i can see only number in message or latest call), and evey thing is turn off in icloud (emails, contact, calendar...)

If i turn everything back on, it ok, but it's happen avery few month.

I don't understand why it's turn of and keep asking my password which is correct.

Thanks for your help.

Regards

Matthieu