How to display custom data array via Twig
Have you added 'front_page_slider to the variables array in your twig template definition?

File...module_name.module

function hook_theme(array $existing, $type, $theme, $path) {
  return [
    'template_name' =&gt; [
          'variables' =&gt; [
           'front_page_slider' =&gt; [],
      ],
    ],
  ];
}