Thanks for the upload, Burgress, I got the file.
It loads just fine. No problem here, but you really need to check the initial scale. This is a map of a larger area, and this needs to be reflected in the Project Settings> Scale.
The location of the DWG-content was also way off from the world origin, which made it hard to see. Please check the scale of the file that I have sent back. Perhaps use Google Satellite maps to get an idea what scale it is, I guess you’re used to doing that already.
If you open the DWG, leave the Subdivision unchecked. Wait a moment until it’s loaded, then unfold the Parent-Null, select the first spline, move the mouse over the editor and press S.
Let me know if there is anything else, I’m happy to look into it.
If you have the latest Illustrator, that might be an option as well, to double-check it, just a thought.
All the best