Why does the iPhone sometimes shake when it doesn't receive information?

1, it may be a spam message, which was intercepted by the system, but you can look for it in the address book.

Another possibility is that you received this short message, but you didn't click to read it immediately. After a while, the system will remind you of the vibration again and tell you that you have received a message, but this message is not the latest, but it was received before.

Extended data:

1.iOS updates the system, and the message will have an "Not in Address Book" function menu to block spam messages.

2. After the system intercepts, you can check in the "Not in Address Book" to see if you want to return to normal SMS.