App notifications disappearing

[AC Question]

I was just wondering, can anyone please explain to me why, when I get an app notification, it only sticks around for about a second before disappearing into the ether, rather than allowing me to check it first? I can't imagine what I would have done, if anything, to cause this to happen, but it's very annoying. I tried turning the phone off and on again, and it did seem to work, but only for about 2 weeks. Thanks in advance.