Category template doesn't show posts for some categories [closed]

Question

I have a site with main categories and subcategories. When you choose a main category, it opens a page with a list of subcategories. When you open a subcategory page it opens a page with a list of posts that belong to that subcategory.

Some subcategory templates don't show the list of posts. Why is that? When I delete the categories and posts and start over it works well, but after 5 test examples it happens again, even with different slugs, category names and posts.

Here is code of my template. I was using a different one before and it also happened with that one.

I think it may be something with the database. Can I fix that somehow?

<?php
if (!category_has_children()) {
        while ( have_posts() ) : the_post(); 
            $categories = get_the_category();
            $last_category = $categories[0];
            foreach($categories as $i => $category)
            {
                if($category->parent == $last_category->cat_ID)
                {
                  $last_category = $category;  
                    the_title();  
                }
            }
        endwhile; 

} else {

    if ( is_category() ) {
        $current_cat = get_query_var('cat');
        $categories=  get_categories('child_of='.get_query_var('cat'));
          foreach($categories as $category) {   
          echo $category->name;
        } 
    } 
?>

And this is the function in functions.php that checks subcategories:

function category_has_children() {
global $wpdb;   
$term = get_queried_object();
$category_children_check = $wpdb->get_results(" SELECT * FROM wp_term_taxonomy WHERE parent = '$term->term_id' ");
    if ($category_children_check) {
        return true;
    } else {
        return false;
    }
}
add_filter( 'init', 'category_has_children' );