How to initialize several UserProviders in Keycloak

I'm having big difficulties when trying to make Keycloak to use default JPA provider that is implemented in Keycloak (package: org.keycloak.models.jpa.JpaUserProviderFactory) alongside with my custom UserProvider.

My user provider is implemented like this:

public class MyCustomUserProviderFactory extends JpaUserProviderFactory {
  @Override
  public String getId() {
    return "demo";
  }

  @Override
  public UserProvider create(KeycloakSession session) {
    EntityManager em = session.getProvider(JpaConnectionProvider.class).getEntityManager();
    return new MyCustomUserProvider(session, em);
  }
}

and MyCustomUserProvider

public class MyCustomUserProvider extends JpaUserProvider {
  private final KeycloakSession session;

  public MyCustomUserProvider(KeycloakSession session, EntityManager em) {
    super(session, em);
    this.session = session;
  }

}

startup.cli

/subsystem=keycloak-server/spi=user:add(default-provider=demo)
/subsystem=keycloak-server/spi=user/provider=jpa:add(enabled=true)
/subsystem=keycloak-server/spi=user/provider=demo:add(enabled=true)

also in META-INF/service i have

org.keycloak.models.UserProviderFactory

with com.demo.keycloak.providers.user.MyCustomUserProviderFactory

So with this implementation and settings, keycloak is started successfully but when I need to access both demo and jpa UserProvider I only get default provider that is in this case demo.

I access UserProvider with:

UserProvider demoProvider = session.getProvider(UserProvider.class, "demo");

but if I execute

UserProvider jpaProvider = session.getProvider(UserProvider.class, "jpa");

I only get null. If I change the default provider in the startup.cli (default-provider=demo) I would then get the jpa but not the demo provider.

Can somebody explan to me how could I have several UserProvider implementation and how can I access to both of them?