As mentioned a note sent to all developers using Comments Box v1 and on our Developer Roadmap, we will upgrade all sites to the new version of the Comments Box in the next couple hours to ensure that Facebook users have access to the latest version across the web. Upon upgrade, ordering of the comments will shift from chronological to showing the most socially-relevant comments first. Also, please note that the upgraded version of Comments no longer supports custom CSS.
Read this update on Facebook by clicking the link below