If you experience that after uploading media items are not showing in the Media Library while physical files were copied into the upload folder, the following instructions should fix the problem.
- Open the Access Viewer.
- Ensure that the Inherit checkbox is set for the Masters node for the sitecore/anonymous user.
- The sitecore/anonymous user should have all allowed security rights for the whole media library.
- Check also that the Everyone group has the same security setup.
I.e. this user (sitecore/anonymous) should have rights for the Media Library where the items are created and for the masters the media items are created from since these actions are performed under this account.