Why didn't the SMS reply in the mobile phone inexplicably decrease a lot?

If it is not caused by my unintentional operation, it can be explained as follows: some mobile phones will delete themselves when the storage reaches a certain amount, but this problem should not occur in today's smart phones. It may be that some software in your mobile phone has the right to read and write short messages, and now many software have the right to read and write deleted information in the memory of your mobile phone. hope this helps