get_delete_post_link( $post->ID ) is blank when logged in as “subscriber”

Your problem might be that the subscriber cannot delete posts. Try the below to find out.

if ( !current_user_can( 'delete_post', $post->ID ) )
{
   echo 'I do not have the privilege to delete posts';
}
else{
     get_delete_post_link( $post->ID );
}

The above might lead you into trouble by letting any user delete any other users post so the below is aimed at letting only the post owner with a subscriber level delete their post or someone with the correct privilege.

          if ( get_the_author_meta('ID') == get_current_user_id() && current_user_can('subscriber') )
          {
            // owner of post and subscriber
            get_delete_post_link( $post->ID );
          }
          if ( get_the_author_meta('ID') != get_current_user_id()  && current_user_can('subscriber')  )
          {
            // not the owner of post and subscriber
            echo 'Not your post';
          }
          else
          {
           // should be ok as not a subscriber and has delete privilages
           get_delete_post_link( $post->ID );
          }