Why do comments on Apple's mobile phone space automatically disappear?

No matter what the mobile phone is, comments in the space will automatically disappear for the following reasons:

The other party has set the comment permission, and the comment will not be displayed until it is approved;

After receiving the comment, the other party deleted the user's comment;

The user's current network is not good, resulting in unsuccessful comments;

The system is busy, and the current user comments are not displayed in time.