Apple SMS is unread but can't be found.

There are the following reasons and solutions:

1. Try to find the "General" option in the device settings and select "Restore" to see if you can restore the history to retrieve unread messages.

2. Try to log in to other accounts to see if any unread messages have been transferred to other accounts.

3. Try to reinstall the system. After backing up the data, you can solve the problem by restoring the factory settings or reinstalling the operating system. This will erase all data on the device, so make sure to back up important information in advance.