In the DefaultEngine.ini, you can actually change bAllowClientSideNavigation to true. This at the very least makes the ANavigationData load on client. It also allows CreatNavigationSystem to create the NavSys. I haven’t tested it just yet, and I’m in 4.9.
EDIT: Just tested it. It works! I know there’s that #if statement, but if you’re game has listen clients then you’ll also compile block.
[/Script/Engine.NavigationSystem]
bAllowClientSideNavigation=True