Autofac: No Scope with a Tag matching Autofacwebrequest

Question

I would like your help to solve the following problem: Imagine that I have a Servicefactory class responsible for creating services (such as srvFact.Create<MyService>()), a Repositoryfactory class responsible for creating repositories (such as repFact.Create<MeuRepositorio>()). Such classes have dependencies, which I will demonstrate through the symbol A <= B, which denotes that A depends on B. For my case I have to: ServiceFactory <= RepositoryFactory.
RepositoryFactory <= DbContext.
That said, imagine that my api uses Automapper to map Viewmodels in Entity Framework Objects and that for certain mappings, it is necessary to access some repository.
What I want: I would like that given a request, as long as that request lives, any request to a Dbcontext instance, return to the same instance, to better control the Dbcontext cycle of activity. Let’s go to the code snippet:

internal void Configure(ContainerBuilder builder)
{
    ConfigureContainer(builder);
    Container = builder.Build();
    RegisterMapping();
}

private void ConfigureContainer(ContainerBuilder builder)
{
    var dbContextType = GetDbContextType();
    var assembly = GetWebApiAssembly();

    // (a) com essa linha o metodo 'RegisterMapping' não consegue resolver a instancia de ServiceFactory
    builder.RegisterType(dbContextType).As(typeof(DbContext)).InstancePerRequest();

    // (b) COM ESSA LINHA, O METODO 'RegisterMapping' consegue obter uma instancia de ServiceFactory
    //builder.RegisterType(dbContextType).As(typeof(DbContext)).InstancePerRequest("myrequest");

    builder.RegisterType<RepositoryFactory>().As<IRepositoryFactory>();
    builder.RegisterType<ServiceFactory>().As<IServiceFactory>();
    builder.RegisterApiControllers(assembly);
}

private void RegisterMapping()
{
    // usando (a) no metodo 'ConfigureContainer' temos um erro:
    // 'No scope with a Tag matching AutofacWebRequest'
    var serviceFactory = Container.Resolve<IServiceFactory>();
    Mapper.Initialize(cfg => ConfigureMapping(cfg, serviceFactory));

    // usando (b) no metodo 'ConfigureContainer' conseguimos resolver ServiceFactory, porém é injetado instancias diferentes de DbContext
    // o que faz com que o mapeamento dentro de 'ConfigureMapping' gere o erro: 
    // 'An entity object cannot be referenced by multiple instances of IEntityChangeTracker'
    //using (var scope = Container.BeginLifetimeScope("myrequest"))
    //{
    //    var serviceFactory = scope.Resolve<IServiceFactory>();
    //    Mapper.Initialize(cfg => ConfigureMapping(cfg, serviceFactory));
    //}
}

The Method Configure(new ContainerBuilder()) is called in Global.asax: DbAccessWrapper.Init(new VaiQueConfig()); where the builder new VaiQueConfig() calls the method Configure passing an instance of ContainerBuilder