If you’d like to exclude certain subcategories in a category archive page, try put the following code in your functions.php:
function exclude_category( $query ) {
if ( $query->is_category( 'myslug' ) && $query->is_main_query() ) {
$query->set( 'cat', '-1,-1347' ); //Add your excluded subcategories ids
}
}
add_action( 'pre_get_posts', 'exclude_category' );
If it’s not the case, we need your code to see the whole picture.