When I used it on Apple, waiting to refresh and restore the backup after jailbreaking, I sometimes encountered a situation where the notification message did not appear. When a friend sends a private message, no notice is very inconvenient, I do not know if you have encountered such a situation in the process of normal use? Here's how I did it.
Apple,
Once opened, click the "Me" column at the bottom, as shown in the picture
Then click the "Settings" button in the upper right corner, as shown in the picture
Then click the "Exit current account" option at the bottom, as shown in the picture
After logging out of the account, log in again to check whether you can receive messages normally.
If the above method still does not work, it is recommended to delete the current application, and then reinstall it should be able to completely solve the problem.