VisualPlugin not loaded not constructed at all

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Hi,

I have problems running a VisualPlugin. When I put its tag under the <visual> tag of a <link>, it seems that it is not read at all when launching gazebo (neither its constructor is called).

Putting the <plugin> tag under <model> or <world> makes the plugin costructor called and an error about uncorrect plugin type (as expected).

When commanding:

 gzserver world/box.world --verbose

Nothing is printed about the plugin

I am using gazebo 9 installed with ROS melodic.

Thanks for any help!

world file:

<?xml version="1.0"?> 
<sdf version="1.4">
  <world name="default">

    <!-- Ground Plane -->
    <include>
      <uri>model://ground_plane</uri>
    </include>

    <include>
      <uri>model://sun</uri>
    </include>

    <model name="box">

      <pose>0 0 5 0 0 0</pose>
      <link name="link">

        <collision name="collision">
          <geometry>
            <box>
              <size>1 1 1</size>
            </box>
          </geometry>
        </collision>

        <visual name="visual">

          <geometry>
            <box>
              <size>1 1 1</size>
            </box>
          </geometry>

          <!--  Not Costructed at all    -->
          <plugin name="visualize_forces" filename="libvisualize_forces.so"/>
        </visual>    

      </link>

      <!--  Costructed, but not loaded, and immediately destroyed (as expected)    -->
      <!--      <plugin name="visualize_forces" filename="libvisualize_forces.so"/>-->

    </model>   

    <!--  Costructed, but not loaded, and immediately destroyed (as expected)    -->
    <!--      <plugin name="visualize_forces" filename="libvisualize_forces.so"/>-->

  </world>
</sdf>

cpp:

#include <gazebo/common/common.hh>
#include <gazebo/rendering/Visual.hh>
#include <gazebo/rendering/rendering.hh>
#include <gazebo/msgs/msgs.hh>

namespace gazebo
{

  class GZ_RENDERING_VISIBLE VisualizeForces : public VisualPlugin
  {
    public: 

    VisualizeForces() {gzmsg << "Constructor" << std::endl;}
    virtual ~VisualizeForces() {gzmsg << "Destructor" << std::endl;}

    void Init() override {gzmsg << "Init" << std::endl;}

    void Load(rendering::VisualPtr _visual, sdf::ElementPtr _sdf ) override
    {
        gzmsg << "Load" << std::endl;
    }
  };

  GZ_REGISTER_VISUAL_PLUGIN(VisualizeForces)
}

I attach the files

C:\fakepath\box.world

C:\fakepath\VisualizeForces.cpp

Fast CmakeLists.txt:

cmake_minimum_required(VERSION 2.8 FATAL_ERROR)

find_package(gazebo REQUIRED)
include_directories(${GAZEBO_INCLUDE_DIRS})
link_directories(${GAZEBO_LIBRARY_DIRS})
list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")

add_library(visualize_forces SHARED src/VisualizeForces.cpp)
target_link_libraries(visualize_forces ${GAZEBO_LIBRARIES})