Message doesn't leave scope of node, if beeing sent in constructor

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Hello, I'm facing a problem, which I can't seem to find any solution for.

Following situation: I'm trying to communicate with multiple vehicles (for prototyping I'm using differenct computers) in one network. I reduced my code to the absolute minimal to show you the problem. The code is the exact same on both of the computers, execpt from the uid_ in the header, which is different.

Steps to reproduce:

• Start node at one computer
• Start other note at the other comptuer

Expected result:

• When starting the second node the callback should show the message on topic /u2u/election at both computers

Actual Result:

• Well, it doesn't show up on the first computer, but only on the one where the node was started from

Other things I tried to debug the problem:

• When opening an extra terminal and echoing the topic with ros2 topic echo /u2u/election the message sometimes pops up and sometimes it doesn't. This applys for both computers, the one where the node is started and the other one. It seems to be random.
• When publishing a message manually via command line the message is received by both terminals echoing the topic and by both nodes

Thanks for your time and let me know if you need any additional information!

u2u_link_minimal.cpp

// include the header of this class
#include "u2u_link/u2u_link_mini.hpp"

/*******************************************************************************************************************//**
 * @brief  Constructor of the ROS node, inherit from Node. Here all ROS specific initializations are done
***********************************************************************************************************************/
U2uLink::U2uLink() : Node("u2u_link")
{
  // Publisher
  init_publisher();

  // Subscriber
  init_subscriber();

  start_election();

  // Initialization of node
  RCLCPP_INFO(this->get_logger(), "Startup init of " + node_name_ + " finished");
}

/*******************************************************************************************************************//**
 * @brief  Destructor
***********************************************************************************************************************/
U2uLink::~U2uLink()
{
}

/*******************************************************************************************************************//**
 * @brief  This method initializes the ROS publisher
***********************************************************************************************************************/
void U2uLink::init_publisher()
{
  pub_elect_u2u_ = this->create_publisher<std_msgs::msg::UInt16>("/u2u/election", 10);
}

/*******************************************************************************************************************//**
 * @brief  This method initializes the ROS subscriber
***********************************************************************************************************************/
void U2uLink::init_subscriber()
{
  sub_elect_u2u_ = this->create_subscription<std_msgs::msg::UInt16>("/u2u/election", 1, 
                                                                  bind(&U2uLink::sub_elect_u2u_cb, this,
                                                                  placeholders::_1));                                                                                                                                                                                                                                                                                                                                     
}

/*******************************************************************************************************************//**
 * @brief  This method initializes the connection to other UAVs
***********************************************************************************************************************/
void U2uLink::start_election()
{
  auto msg = std_msgs::msg::UInt16();
  msg.data = uid_;
  pub_elect_u2u_ -> publish(msg);
}

/*******************************************************************************************************************//**
 * @brief  Subscriber callback for /u2u/election
 * @param  common::msg::UInt16::SharedPtr
***********************************************************************************************************************/
void U2uLink::sub_elect_u2u_cb(const std_msgs::msg::UInt16::SharedPtr msg)
{
  cout << msg->data << "received in cb " << endl;
}


/*******************************************************************************************************************//**
 * @brief  the main function which initializes and starts the node object 
 * @param  int argument count, char ** argument values 
 * @return exit code
***********************************************************************************************************************/
int main(int argc, char ** argv)
{
  rclcpp::init(argc, argv);
  rclcpp::executors::MultiThreadedExecutor executor;
  auto n = std::make_shared<U2uLink>();
  executor.add_node(n);
  executor.spin();
  rclcpp::shutdown();
  return 0;
}

u2u_link_minimal.hpp

#ifndef U2U_LINK_MINI_HPP
#define U2U_LINK_MINI_HPP

// C system header
#include <stdint.h>

// C++ STL header
#include <iostream>
#include <string>

#include "rclcpp/rclcpp.hpp"

#include "std_msgs/msg/u_int16.hpp"


// usings
using namespace std;

class U2uLink : public rclcpp::Node
{
  public:
    // Con-/De-structor
      U2uLink();
      ~U2uLink();

  private:
    // General methods
      void init_publisher();
      void init_subscriber();
      void start_election();

    // Subsriber callbacks       
      void sub_elect_u2u_cb(const std_msgs::msg::UInt16::SharedPtr msg);

    // Callback groups
      rclcpp::callback_group::CallbackGroup::SharedPtr cb_group_clt_;

    // Publisher
      rclcpp::Publisher<std_msgs::msg::UInt16>::SharedPtr pub_elect_u2u_;

    // Subscriber
      rclcpp::Subscription<std_msgs::msg::UInt16>::SharedPtr sub_elect_u2u_;

    // General variables
      string node_name_ = "u2u_link"; 
      uint16_t uid_ = 1002;
};

#endif