While loop in functions.php outputting the_title() of each post on frontpage

I have the following code on the website:

$args = array(
    'posts_per_page' => -1,
    'post_type' => 'gyorshirek',
);

$loop = new WP_Query( $args );
$wp_query = $loop;

if ( $loop->have_posts() ): 
    while ( $loop->have_posts() ): $loop->the_post(); 

    $custom_fields = get_post_custom( $loop->ID );
    $cpost        = get_post( $custom_fields['ceg_megadasa_gyorshirek'][0] );
    $cpost_custom = get_post_custom( $cpost->ID );


    

    $ticker = $cpost_custom['feed_id'][0];
    
    $url = 'https://api.portfolio.hu/chart?ticker=' . $ticker . '';
    $token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJUxZF6c2RlZsOzcnVtIGFkYXRzem9sZ8OhbHRhdMOhcyIsImlhdCI6MTUxNjIzOTAyMiwiaXNzIjoicG9ydGZvbGlvLmh1IiwiZXhwIjoxNjcyNTI3NTk5LCJzdWJzIjp7Im1pIjoiMVkifX0.LPeFFyLUJmIw2xbRPcJjHhNaGQE6daI4NUaMJtL76PU';
    $args = array(
        'headers' => array(
            'Authorization' => 'Bearer ' . $token,
            'Content-type' =>'application/json; charset=UTF-8',
        ),
    
        
    );
    
    $response = wp_remote_get($url, $args);
    $body     = wp_remote_retrieve_body( $response );
    $http_code = wp_remote_retrieve_response_code( $response );
    $formatted_json = json_decode($body, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
    if (isset($formatted_json['change_percent'])) {
        $change_percent = $formatted_json['change_percent'];
    
    } else {
        $change_percent = 0;
    }
    
    if (isset($formatted_json['ticker'])) {
        $stockticker = $formatted_json['ticker'];
    
    } 
    
    if (isset($formatted_json['last'])) {
        $lastprice = $formatted_json['last'];
    
    } 
    
    
    $field_key = "field_60df782a45b20"; // "ceg_valtozas"
    $value = $change_percent;
    
    update_field( $field_key, $value);
        
    wp_reset_postdata();
    
     endwhile; 
     endif;

I only want this code to be used to update a field of a custom post type.
The code works, however it breaks my front page by outputting the title of each post.

I can’t figure out what is causing this inside this loop. If I delete it, the problem goes away.

Any ideas?