When I go to clear temporary alerts like he active card check, the clear alert comes up for a second. The. It spins away on its own. After that, clicking he “x” just makes it spin. I can’t actually clear these! Hard closing the app and trying again allows the clear button come up again however it again quickly disappears on its own. I’m on 11.3 beta 2.
I have the same problem, seemingly randomly. Sometimes it behaves as you describes (just alternates between ‘x’ and ‘clear’, never going away), and sometimes it works properly. I don’t get enough alerts to figure out if there’s a pattern.