The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
@Jip said in Offline Line Campaign/Skirmish:
You need to host at least one (coop) game through the client. That will retrieve the file in question. Then you can play offline again.
The game files are not included with the launcher by default.
Thanks for the help Jip, I appreciate it.