The cause is that the host controls too much, and the plane crashing is needed for players to properly spawn. If the plane crash position does not get set, saves will not work properly. This is why you see some NREs and such. I've been trying a bunch of different ways, but sadly it isn't as easy as it was originally. Essentially we have to emulate the client skipping the plane crash in some way, and then saving that. You can load previous saves from a client that has skipped the plane crash and saved it successfully, but the saving through Oxide isn't quite solid yet.