QPluginLoader instance returns null

Greeting

I created plugin with Qt (5.6.2) and trying to load it but it returns null all the time. I checked several question and also tried the solutions but it didn't work for me.

Can you take a look of the following code and see whats wrong?

DeviceManager.hpp

#ifndef DEVICE_MANAGER_HPP
#define DEVICE_MANAGER_HPP

#include <QtCore>
#include <string>

using namespace std;

class DeviceManager
{

public:
    virtual ~DeviceManager() {}

    virtual bool initialize() = 0;
    virtual string getBrandName() = 0;

};

QT_BEGIN_NAMESPACE
Q_DECLARE_INTERFACE(DeviceManager, "com.some.address/1.0")
QT_END_NAMESPACE

#endif //DEVICE_MANAGER_HPP

DeviceManagerImpl.hpp

#ifndef DEVICE_MANAGER_IMPL_HPP
#define DEVICE_MANAGER_IMPL_HPP

#include "DeviceManager.hpp"

#include <string>
using namespace std;

class DeviceManagerImpl : public QObject, public DeviceManager
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "com.some.address/1.0")
    Q_INTERFACES(DeviceManager)

public:
    DeviceManagerImpl();

    //Override Method
    bool initialize();          //Have implementation in cpp file
    string getBrandName();      //Have implementation in cpp file

private:
    ...

};

#endif //DEVICE_MANAGER_IMPL_HPP

Pro File

QT       += core gui sql

TARGET = Device-Manager
#TARGET = $$qtLibraryTarget(Device-Manager)
TEMPLATE = lib
CONFIG += plugin


SOURCES += \
    ...

HEADERS += \
    ...

DISTFILES += Device-Manager.json

unix {
    target.path = /usr/lib
    INSTALLS += target
}

And this is how i try to load the plugin in my main process.

QPluginLoader * pluginLoader = new QPluginLoader(pluginPath.c_str());
QObject * plugin = pluginLoader->instance();

if (plugin)
{
    deviceManager = qobject_cast<DeviceMAnager *>(plugin);
    return true;
}
else
{
    delete pluginLoader;
    return false;
}

Im using QT 5.6.2 and QT Creator and MinGW 32bit.

EDIT 1: I found the reason but i have no idea why it cause the problem, Im using library that is linked to project but when i use its function, The instance returns null.

LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/MSXFS.lib
INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)/INCLUDE

I also have no compile or linker error. Can anyone tell me what wrong here?

EDIT 2:

The following configs of library and plugin in CMakeList.txt work perfectly fine when i make the project with Visual Studio. (Made with CMake)

ADD_DEFINITIONS(${QT_DEFINITIONS})                                                                                      
ADD_DEFINITIONS(-DUNICODE -D_UNICODE)                                                                                       
ADD_DEFINITIONS(-DQT_PLUGIN)                                                                                
ADD_DEFINITIONS(-DQT_SHARED)                                                                                            
ADD_DEFINITIONS(-DQT_DLL)                                                                                           
ADD_DEFINITIONS(-DQT_LARGEFILE_SUPPORT)
ADD_DEFINITIONS(-DQT_THREAD_SUPPORT)

INCLUDE_DIRECTORIES(
    ${STANDARD_XFS_DIRECTORY}/INCLUDE
)

LINK_DIRECTORIES(
    ${STANDARD_XFS_DIRECTORY}
    ${STANDARD_XFS_DIRECTORY}/LIB
)

SET(XFS_LIBS
    MSXFS
    xfs_conf
    SSIDLL
)

TARGET_LINK_LIBRARIES(Device-Manager 
    ${XFS_LIBS}
)

And this is the configs of library and plugin in .pro file in Qt Creator with MinGW which is not working when i use the library.

QT  -= gui
QT  += core sql

TARGET = Device-Manager
TEMPLATE = lib
CONFIG += plugin
CONFIG += c++11

DEFINES += DEVICEMANAGER_LIBRARY

INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)
INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)/INCLUDE
message(Include : $${INCLUDEPATH})

LIBS += $$(STANDARD_XFS_DIRECTORY)/SSIDLL.lib
LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/MSXFS.lib
LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/xfs_conf.lib
message(Lib : $${LIBS})

So i can say the code it self is fine and i'm definitely missing some configs in .pro file.

PS1: Plugin and the application that load the plugin, Both have INCLUDEPATH and LIBS of the library in their pro file.

PS2: The application and the plugin both are in debug mode

PS3: I dont get any compile error or linker error during compile.

EDIT 3:

I made simple console application and included my library header and lib file and called the function and this is the error i get when i run the application. So it must be it. But seriously why!!!

The Code:

LPWFSRESULT result = new WFSRESULT();
WFSFreeResult(result);

PS: The library is from trusted source and it work perfectly with Visual Studio.

Thanks in advance.