I am also having this issue. I was not having this problem yesterday, and i played ArmA 3 quite normaly. But today, i can't do it because of this "loading core configs" issue. I hope bohemia interactive will fix it soon. Meanwhile, we can try on playing some older versions of the game (wich i believe, don't have those issues). If you bought arma 3 by the steam store (such as i did), you can right click on the game's shortcut inside your steam's game library and then select "properties", and then "betas" then, search on the internet for the code of a recent, but not very recent arma 3 update. Once you have the code you can simply insert the code in the "beta acces code" space, then hit "check code". That way, ArmA 3 should downgrade back to the version referent to the code. i'm gonna do it myself right now and see if it works. You can try it yourself as well. I Hope i helped.