First step in debugging things you don't understand is to create a minimal example from scratch, just to see if there's a problem directly with SFML, or if it's just within your code, e.g.:
#include <SFML/Graphics.hpp>
int main()
{
sf::RenderWindow window(sf::VideoMode(1024, 768), "Hello World");
sf::Font font;
font.loadFromFile("fonts/arial.ttf");
sf::Text text;
text.setFont(font);
while(window.isOpen())
{
sf::Event event;
while(window.pollEvent(event))
{
if(event.type == sf::Event::Closed)
window.close();
}
window.clear();
window.draw(text);
window.display();
}
}
If that does work without problems, then it's something within your structure.
Also if you actually try to draw a text on top of the door rectangle, then you can't draw the text first and then the rectangle, otherwise the rectangle will cover up the text.
Edit: Not sure if this could be part of the problem, but since you have the sf::Font as member of the Doors class, you load the font for every door instance, thus you end up with x copies of the same font. It's not really good to do this, but I'm not sure if it could cause such a problem.