Hey Andre,
It seems like this plugin `Joobi - Secure Activity` blocked that retrieve language content from backend, once I disable it, it can retrieve the language file correctly.
But for now I already enabled it back that plugin from your backend.
Can you try update one of your site language from Easysocial language backend and see is it work correctly?
Note : For now I am not really sure why this happen related this plugin, so you have to disable this when you click discover or update button from Easysocial language page.