"Your connection to the Steam servers has been lost."

[Starker]

This appeared spontaneously and the game is now unplayable:

https://i.imgur.com/0R3JIgw.jpg

No other games are affected.

[Codex]

Yeah I can see from your screenshot you aren't running our mod. This is a result of the game having DRM always on, and that will never change. My recommendation is try to ensure for online play doing everything in your power to stabilise your connection eg router reset.

For campaign and stuff you can always switch steam to offline mode.

Sorry that this probably doesn't seem helpful