Same thing.
Just updated the patch, verified files. logged out of Steam account and back in, verified files again, no mods, and “Unable to login, please restart or try again later. Continuing in Offline Mode in which single-player mode is available.”
Second time this happened. Some sort of information in regards to whether or not this is an issue communicating with Valve (Steam) Services or something would be GREATLY appreciated as some of us have VERY LIMITED TIME to play.
Edit: Since I can’t go online, I GET NONE OF MY DLC CONTENT!
Edit 2: Suddenly back up. Communication is key. At lease a confirmation that an issue was looked at and resolved or something. This is a problem with the gaming development community (and IT in general): No communication to users.