There's nothing like alert disappearance om your device except you have a malicious physhing attack currently running onnyour device unknowingly to you, you can also try check your alert notification settings on their page and on your mobile device as well, the function might have been disabled, lastly, if you constantly receives alert from them and you don't cluck to open them, theyay reduce the numbers of alerts being sent and if not changes, they may decided to stop sending you alert, if this happens to be the case, try and disable the alert notification and enable it back to opt you in again.