Still not fixed sadly and haven't seen any answers from the Plutonium team, either. I've lost big chunks of progress twice now. Playing a public game after changing stuff in create-a-class, scorestreaks, profile, etc seems to help 'save' your progress before you exit the game, but I don't think it's a guarantee.
Having profile backups (like a "username".json file) might help, but I don't know if that's do-able with Plutonium.