Lines ALSO Duplicate when Duplicating an Artboard
When an artboard is duplicated, all of the lines and shapes should be duplicated with the artboard. There is a bug or what appears to be a bug in Version 188.8.131.52 where strokes that are components are not included when an artboard is duplicated. They must be manually selected and copied to the duplicate artboard.
Thanks for filing a ticket! This seems like a bug and not a feature request, so you should definitely file this on the Community Support Forum. https://community.adobe.com/t5/adobe-xd/bd-p/xd?page=1&sort=latest_replies&filter=all