SharePoint Online is always improving how we deliver our service.  As part of delivering updated features for social actions, like following sites and documents, we are making some changes that impact how some of our existing APIs return data.

The affected API set is the social.following APIs (documentation) – specifically the followed count API (http://<siteCollection>/<site>/_api/social.following/my/followedcount) will no longer return results.

In the future these existing social APIs will be superseded by the Microsoft Graph APIs for social actions and may be deprecated.  For an example API, see the Followed Sites API in Microsoft Graph, currently in beta documentation).