Service not responding with MultiThreadedExecutor executor

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I'm attempting to create a service with the MultiThreadedExecutor executor

My goal is to eventually add call backs to a rclcpp::CallbackGroupType::MutuallyExclusive callback group.

However, the service is never reached when I change the executor to MultiThreadedExecutor executor.

It does work when I use rclcpp::spin(this);

auto callbackGroup = this->create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);

std::function<void(
    const std::shared_ptr<interface::srv::Reader::Request> request,
    std::shared_ptr<interface::srv::Reader::Response> response)> readerCallBack;

std::function<void(
    const std::shared_ptr<interface::srv::Writer::Request> request,
    std::shared_ptr<interface::srv::Writer::Response> response)> writerCallBack;

readerCallBack = bind(&service::readFrom, 
    std::placeholders::_1,      // Corresponds to the 'request'
    std::placeholders::_2,      // Corresponds to the 'response'
    file);

writerCallBack = bind(&service::writeTo, 
    std::placeholders::_1,      // Corresponds to the 'request'
    std::placeholders::_2,      // Corresponds to the 'response'
    file);


*reader = this->create_service<interface::srv::Reader>(
    readerTopic,         
    readerCallBack,
    rmw_qos_profile_services_default);

//create service to write/read to file
*writer = this->create_service<interface::srv::Writer>(
    writerTopic,
    writerCallBack,
    rmw_qos_profile_services_default);

rclcpp::executors::MultiThreadedExecutor executor;
executor.add_node(this);
executor.spin();  //doesnt respond

//rclcpp::spin(this);  //works

This seems to work:

rclcpp::executors::MultiThreadedExecutor executor;
executor.add_node(servicePtr->get_node_base_interface());
executor.spin();

However, it fails when I add the callback group:

*reader = this->create_service<interface::srv::Reader>(
    readerTopic,         
    readerCallBack,
    rmw_qos_profile_services_default,
    callbackGroup);

//create service to write/read to file
*writer = this->create_service<interface::srv::Writer>(
    writerTopic,
    writerCallBack,
    rmw_qos_profile_services_default,
    callbackGroup);