Segmentation fault while drawing a sf::Text

This function cause the segfault :

void SFMLDisplayManager::displayButton(TextElem const &button)
{
  sf::RectangleShape buttonShape(sf::Vector2f(button.sizeX, button.sizeY));
  sf::Text shapeText;
  ConvertColor convert;

  convert.color = button.color;
  if (button.text != "")
  {
    shapeText.setCharacterSize(button.FontSize);
    shapeText.setFont(this->_font);
    shapeText.setPosition(button.pos.x, button.pos.y);
    shapeText.setColor(sf::Color::Red);
    shapeText.setString(button.text);
    std::cout << "before" << std::endl;
    this->_window->draw(shapeText);
    std::cout << "after" << std::endl;
  }
  buttonShape.setFillColor(sf::Color(convert.colors.r, convert.colors.g, convert.colors.b, convert.colors.t));
  buttonShape.setPosition(button.pos.x , button.pos.y);
  this->_window->draw(buttonShape);
}

And I use it a lot to draw differents other things. I even send the same button, but at the start of my program and it works fine. My valgrind is empty,I just go a

==17529== Jump to the invalid address stated on the next line
==17529==    at 0x5CD1E: ???
==17529==  Address 0x5cd1e is not stack'd, malloc'd or (recently) free'd
==17529== 

when the segfault occure.

If a run it with gdb I got

0x00007ffff5a5f645 in FT_Render_Glyph_Internal () from /lib64/libfreetype.so.6

When I print all the information of button, all information are good.

Have any idea why it segfaults ?