Problem when linking out to separate file within foreach loop

As far I’ve known get_template_part() function does not work with foreach loop. So we need to use locate_template() function to this case. This is your customized category template code. Put it there –

<?php
/**
 * Category Template: Custom
 */

get_header(); ?>
    <div id="content" class="site-content container <?php echo codilight_lite_sidebar_position(); ?>">
        <div class="content-inside">
            <div id="primary" class="content-area">
                <main id="main" class="site-main" role="main">
        <?php 
        $cat = get_category( get_query_var( 'cat' ) );
        $cat_id = $cat->cat_ID;
        $child_categories=get_categories(
        array( 
            'parent' => $cat_id,
            // Uncomment the below line if you want empty category to appear on the list. 
            // 'hide_empty'   => 0
            )
        ); 
        if (!empty($child_categories)) : $count = 0; ?>

                    <header class="page-header">
                        <?php
                            the_archive_title( '<h1 class="page-title">', '</h1>' );
                            the_archive_description( '<div class="taxonomy-description">', '</div>' );
                        ?>
                    </header><!-- .page-header -->

                    <div class="block1 block1_grid">
                    <?php
                    foreach(array_chunk($child_categories, 2) as $item) {
                        echo '<div class="row">';
                        foreach ($item as $child) {
                            // get_template_part( 'template-parts/content-grid' );
                            include( locate_template( 'template-parts/content-grid.php' ) );
                        }
                        echo '</div>';
                    }
                    ?>
                    </div>

                <?php else : ?>

                    <?php get_template_part( 'template-parts/content', 'none' ); ?>

                <?php endif; ?>

                </main><!-- #main -->
            </div><!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>