After using logcat I see this OpenGL error after a resume:
sfml-error: An internal EGL call failed in EglContext.cpp (189) : EGL_BAD_SURFACE, an EGLSurface argument does not name a valid surface (window, pbuffer, or pixmap) configured for rendering
This is how I create the window:
sf::ContextSettings settings;
sf::VideoMode mode = sf::VideoMode::getDesktopMode();
sf::Window win(mode, "SFAppDelegate", sf::Style::Fullscreen, settings);
Does that seems correct ?