This option automatically removes duplicate posts from the page. The feature was designed to work on static pages. If you use pagination, including the Load More button and Infinite Load, it will generate duplicates on the second page. For this case, you have to use the offset feature. Read more about it, here.
This image is an exemplification on how two blocks using the same settings can display duplicate posts:
You can enable the Unique Articles feature for each page. The option is available in the page editing section:
After enabling this option, update the page and check the results: