IHostMigratable

A native interface for state that UPROPERTY(SaveGame) cannot express. Implement it on migrated actors, their components, PlayerStates, the GameMode or the GameState.

#include "HostMigratable.h"

UCLASS()
class AMyActor : public AActor, public IHostMigratable
{
	GENERATED_BODY()

public:
	virtual void SaveMigrationState(FArchive& Ar) override
	{
		Ar << Waypoints;
		Ar << TargetId;
	}

	virtual void RestoreMigrationState(FArchive& Ar) override
	{
		Ar << Waypoints;
		Ar << TargetId;
	}

	virtual void PostMigrationRestore() override
	{
		// Every migrated actor exists now.
	}

private:
	TArray<FVector> Waypoints;
	FGuid TargetId;
};

Function	When
SaveMigrationState(FArchive&)	On the host, when a snapshot is built, after SaveGame properties are written.
RestoreMigrationState(FArchive&)	On the new host, before BeginPlay. Must read exactly what was written.
PostMigrationRestore()	On the new host, once every migrated actor has been restored.

Object references written to the archive (Ar << SomeActorPtr) are stored by migration id and resolve on the new host, the same as SaveGame references. You can also store an FGuid and look it up with UHostMigrationBlueprintLibrary::FindActorByMigrationId.