IPhone 4S Delayed Text Notification?

Okay, in the last two months I've noticed that my iPhone 4S is not notifying me of texts right away when it's locked. I'll get a text then when I unlock the phone and go to look at it it'll say it's from anywhere between 7 and 20 minutes ago. I'm just wondering if anyone knows how to fix this. I've already tried holding down the home and power buttons to restart it. I don't know how I feel about restoring it.

Added (1). I ALREADY TRIED RESTARTING IT. IT DOESN'T Help.

Happens to me android as well try restarting

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