Never seen this before. Doing a search on details in your OP got me to this:
GameConfig: Couldnt connect to host -
reddit post, from that it seems that EAC *may* be involved but its hard to say without knowing more info or details of your setup.
Unable to get backing store! - Found
this post relating to an issue with OSX, but that's about it..
As a start have you tried verifying your game files? Maybe try that if you havent already.
Also, do you have any software firewalls/security programs like Bitdefender? I see posts about EAC and software like this not getting along all the time in these forums. Might also be affecting you perhaps? (As above)
Otherwise if both those posts don't help you out at all maybe raise it in the bug reports so it gets looked at by Facepunch
Hope that helps!