Why can't the mobile phone always receive short messages, but it can always be received after it is turned off and turned on?

Do you say the battery shuts down automatically when it is dead, or do you shut it down yourself?

One possibility is this:

SMS has a maximum time limit.

For example, I set this maximum time limit to 24 hours.

So if my texter doesn't call within 24 hours,

After this time, the message will be invalid.

You wouldn't understand.