it can often occur in drupal but not other CMS systems.after some time, you may find newly added content can not be showed to non-authenticated users.

the reason while it happes is when you install or remove some module in drupal. it breaks the user access permission table. especially those access permission modules.

what you need to do is rebuild site content permissions.
which located in The node access table.
before you rebuild you may would like to backup the node access table so that the rebuild of permission can be undo.

This will wipe all your current node permissions and rebuild is based on current access settings.
This action cannot be undone in administer panel.

steps to solve this problem:
1. login as administrator.

2. locate to Content management, Post settings

3. click on Rebuild permissions button then click again to confirm.

4. verify the permission.