By any chance does it only happen when you pick the phone up? If so, maybe you have this feature on?
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Forgot about this haha
...so if he picked up the phone and felt it there should be something there to see!
My first thought was this as well since I use this feature but the purpose of the feature is to alert you to a notification that you missed so if he picked up the phone and felt it there should be something there to see!