Well assuming that you already checked your internet connection and came to the conclusion that your internet is fine, I need to ask: Do you share your Steam account via family share? Cos If someone logs in with your account while you are ingame, you get always disconnected on steam (as long as you didn't reach a certain high "steam rank" if I am not mistaken).
If Relic servers would have an issue, then there would be a different pop-up and not "You have been disconnected" I think