If it's there even without the app, it should definitely be a bug or it's the navigation bar. Bro, when you use gesture navigation, a bar will be there. You sure it's not that? Does clicking on that bar opens Samsung wallet? If not, it can't be associated with the wallet app.
Have you tried turning off "gesture hint" by going to Navigation bar inside phone settings?(just search "gesture hint" inside settings).
It works for wallet when we swipe up. I was pretty confident it's not related to wallet as it was showing even after the app was uninstalled. It was gesture hint, which I disabled and its gone.
