This sounds very bizarre, but I will tell you that I had some slightly similar issues with my Mac distribution of the game. I never reported the problem, because I could not find that anyone else was having it.
I use the Steam client, and I tried switching to the base client, but it was doing the exact same thing. Extremely odd. It turns out, it was probably some issue with a recent patch being somehow corrupted on the way from the server. What fixed it for me was, unfortunately, to redownload the unpatched game from Steam, and patch it up again. I had to do this several times before it finally worked, and I haven't had any issues since, but I'm not entirely sure that this is a good solution.
Hope you can get it working again!
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