I have never had an easy go of exporting Civ 3D dwgs to previous versions. Either it crashes out entirely, or the exported dwg throws a prompt in the previous version that it cannot be saved as it was created with an earlier version. What's the point of exporting if you can't work with the file in the version you exported it to? Or id this another one of AutoDesk's forced upgrade schemes?
I really don't have a question here... just venting, I guess.
FYI, my office is on 2018, but the client (government) is on 2013.