Notifications disappearing once phone is unlocked?

I use the fingerprint scanner to unlock my phone so usually only get a very quick peek at notifications on the lock screen. Once the phone is unlocked these notifications don’t seem to show in notification centre.

Is there a reason for this?

Funnily enough the reason I ask is because I was trying to show a friend the little fish emoji that popped up with the payment for our fish and chips takeaway- but it had gone before I had the chance haha