My self and @Phantasmos have experienced issues logging into the Forum yesterday and today. Luckily I was still logged in on my computer.
If you open a private window or Incognito window and try to log in with Facebook you get the following error
Currently I have been in contact with Phantasmos and as of yesterday he has not been able to login and I am now seeing the issue having tested different routes.
I tried being completely logged out of Facebook before attempting to log in as well as different browsers, IE, FireFox, Edge and Chrome. I also received the same error on my Samsung Note5.