I ended up using UE4’s handy SaveGame class to store the data and restore it back after login. Works really well
I first tried enabling seamless travel for when the offline client joins a server, but it doesn’t seem to work. It was unable to join the server. I’m under the impression that seamless travel is only meant to be used when you’re ALREADY connected to a server, but not when you’re joining one. Or maybe I made a mistake somewhere?