Covid Exposure Notifications disappear
I have an iPhone SE (the 2020 version). I have downloaded the NHS Covid Test and Trace app. A couple of times in the last few weeks a message has appeared (are they called Notifications?) on the screen saying that I have come into contact with someone with covid. I've touched the message to see what it says (thinking that it will open the NHS Covid app for more info) but nothing happens and the notification disappears. Then a minute later another notification appears saying something about they have calculated that there is no risk. Again I click the notification, it again disappears.
I've opened the NHS app expecting to see notifications / messages / further info, but there isn't anything.
I've swipped down from the top of the iPhone screen to display 'Notifications Centre' but the covid notifications are not displayed.
I've done a little research and seen in the news in October that the NHS app could generate 'ghost' disappearing messages, but the app has been updated to stop this. I beleive iOS updates app automatically? I can't find a way to manually update the app.
What's going on?
Do I even need the NHS app? Do Apple phone now come with built in covid exposure tracking? I've read something about Exposure Notification, but I can't find an app on my phone called that and nor can I find it Settings.
iPhone SE, iOS 14