This has been Facebook's MO for almost 5 years now. What Social Fixer was doing in particular is among a class of applications that Facebook has always deleted

This has been Facebook's MO for almost 5 years now. What Social Fixer was doing in particular is among a class of applications that Facebook has always deleted or banned as soon as they noticed them. I've had applications with 5-10MM MAU deleted without warning and know dozens of folks with similar stories. That's life developing for Facebook. Don't be under any illusions if you decide to play in their sandbox.