Facebook Messenger is the app that's having this issue for me at the moment, but Tinder was doing it a few weeks ago then magically resolved itself (or I did something unknowingly). Someone will send me a Facebook message, my lock screen will light up, I'll briefly see the notification, then it'll clear and it'll be gone from Notification Centre. The message has never been marked as read (I was curious if someone was snooping my account). I've rebooted my iPhone, quit Facebook Messenger and turned notifications off/on again. Anyone experienced something like this with an app? What was the solution?