Facebook has a bug for a while and it happens for certain users only. The bug is that it does not display the list of the apps you have blocked.

It sounds not a biggy one, but if you block an app on Facebook you can no longer have the option to unblock it, you need first to retrieve the apps you have blocked and then click unblock.

So you are stuck and you can no longer access the app.

I've contacted developer support from Facebook and they told me it's not related to them and to contact Facebook Help Center.

It's been a few months and still no response from Facebook.

Maybe someone around here can trigger some investigation, who knows...

Thanks.