Location: Appearance > Customize > Front Page
Almost a dozen widgets are bundled in the theme ColorMag which are used to display various posts along with its featured image. These widgets display latest posts or posts from some specific category. So, when many widgets are used in the same page like the Front Page of ColorMag Pro demo site, it is likely that the posts are repeated. That means same posts can be displayed in several places by the different widgets.
To avoid same post repeating over and over in the same page, under the Unique Post System, you can use checkbox to show show posts only one time in a page.