Pagination Not Working on `WP_Query` Archive Page

Note that with a custom WP_Query class instance like the $homePageArticles in your case, you should pass the max_num_pages property of the class instance to paginate_links():

paginate_links( array(
    'total' => $homePageArticles->max_num_pages,
) )

However, that alone will not work with custom offset which breaks the pagination, hence for example you got this issue:

it just shows the same posts on each page

But it can be fixed and it’s quite easy:

1. Calculate the offset based on the current page number and pass the offset to WP_Query:

   // Current page number.
   $paged = max( 1, get_query_var( 'paged' ) );
   
   $per_page     = 18; // posts per page
   $offset_start = 9;  // initial offset
   $offset       = $paged ? ( $paged - 1 ) * $per_page + $offset_start : $offset_start;
   
   $homePageArticles = new WP_Query( array(
       'posts_per_page' => $per_page,
       'offset'         => $offset,
       'post_type'      => 'articles',
       // No need to set 'paged'.
   ) );
   

2. Recalculate the max_num_pages property and pass it to paginate_links():

   $homePageArticles->found_posts   = max( 0, $homePageArticles->found_posts - $offset_start )
   $homePageArticles->max_num_pages = ceil( $homePageArticles->found_posts / $per_page );
   
   while ( $homePageArticles->have_posts() ) ...
   
   echo paginate_links( array(
       'current' => $paged,
       'total'   => $homePageArticles->max_num_pages,
       ...
   ) );
   

But then, if you’re making the custom WP query in an archive template, e.g. archive-articles.php (archive-<post type>.php)

Then you should just forget that custom WP query.

And instead, use the pre_get_posts hook to filter the main WP query args (to set the custom offset), then use the found_posts hook to make sure we have the correct max_num_pages value, then just loop through the posts in the main query.

1. In the theme functions file:

   function my_pre_get_posts( $query ) {
       if ( ! is_admin() && $query->is_main_query() &&
           is_post_type_archive( 'articles' )
       ) {
           $query->set( 'offset_start', 9 );
           $query->set( 'posts_per_page', 18 );
       }
   
       if ( $offset = $query->get( 'offset_start' ) ) {
           $per_page = absint( $query->get( 'posts_per_page' ) );
           $per_page = $per_page ? $per_page : max( 1, get_option( 'posts_per_page' ) );
   
           $paged = max( 1, get_query_var( 'paged' ) );
           $query->set( 'offset', ( $paged - 1 ) * $per_page + $offset );
       }
   }
   add_action( 'pre_get_posts', 'my_pre_get_posts' );
   
   function my_found_posts( $found_posts, $query ) {
       if ( $offset = $query->get( 'offset_start' ) ) {
           $found_posts = max( 0, $found_posts - $offset );
       }
   
       return $found_posts;
   }
   add_filter( 'found_posts', 'my_found_posts', 10, 2 );
   

2. Then in your archive template:

   // No need for the "new WP_Query()".
   while ( have_posts() ) : the_post();
       ... your code.
   endwhile;
   
   // No need to set 'current' or 'total'.
   echo paginate_links( array(
       'prev_text' => 'NEWER',
       'next_text' => 'OLDER',
       ...
   ) );
   

And actually, with the custom functions in #1 above, you could simply use the custom offset_start arg with any WP_Query instances:

// Current page number.
$paged = max( 1, get_query_var( 'paged' ) );

$homePageArticles = new WP_Query( array(
    'posts_per_page' => 18,
    'offset_start'   => 9, // <- set this
    'post_type'      => 'articles',
    // No need to set 'paged' or 'offset'.
) );

while ( $homePageArticles->have_posts() ) ...

echo paginate_links( array(
    'current' => $paged,
    'total'   => $homePageArticles->max_num_pages,
    ...
) );