I removed some of the groups from the 'Featured Groups' pane in my organization settings. I wanted to add some back, but it's only searching groups listed in my organization and not any of the public groups like Esri.
Did I miss a setting? The options for allowing members of the group to search online content is enabled.
It will only search for groups in your organization, and in general, it's probably a good idea to point at groups you control. Also, there is an option for "Esri Default" in the list as well.