This article explains what to do in case the News Feed is not showing recent content, for example when a newly created blog post does not show up in recent activity.
Navigate to Admin Console > System > Settings > News > Rebuild steam:
Select the news feed you want to rebuild from the dropdown:
and click "Rebuild". The stream will start the rebuilding process:
Once the rebuild completes successfully, the message will disappear, and the page will be ready for another rebuild if needed. Be aware that news streams with a lot of content may take minutes and even tens of minutes to complete the rebuilding.