准备好的语句停止写入 Mysql 表

Question

该脚本工作了大约 6 个月，但突然停止写入 mysql 中的 3 个表之一。 我对此不知所措，似乎无法解决问题。 脚本写入 client_license 和 clients_notes 表，但不会在其生命周期内写入客户端表。 正如我所说，直到 2 周前，它确实运行良好。 代码没有任何变化，我似乎在数据库上找不到任何问题。

<?php
session_start();
if (!isset($_SESSION['loggedin'])) {
    header('Location: index.html');
    exit();
}
if( $_SESSION['access'] != "admin") {
    session_destroy();
    header("location: index.html");
}
?>
<?php
$DATABASE_HOST = 'localhost';
$DATABASE_USER = '***';
$DATABASE_PASS = '***';
$DATABASE_NAME = '***';
$con = mysqli_connect($DATABASE_HOST, $DATABASE_USER, $DATABASE_PASS, $DATABASE_NAME);
if (mysqli_connect_errno()) {
die ('Failed to connect to MySQL: ' . mysqli_connect_error());
}
if (!isset($_POST['clients_initials'], $_POST['clients_name'], $_POST['clients_nickname'], $_POST['clients_surname'], $_POST['clients_id_nr'], $_POST['clients_profession'], $_POST['clients_tel'], $_POST['clients_tel_alt'], $_POST['clients_email'], $_POST['clients_address_complex'], $_POST['clients_address'], $_POST['clients_suburb'], $_POST['clients_town'], $_POST['clients_province'], $_POST['client_license_nr'], $_POST['client_license_expiry'], $_POST['client_license_code'])) {
    header("Location: statusclient1a_admin.php");
    die();
}
if ($stmt = $con->prepare('SELECT * FROM clients WHERE clients_id_nr = ?')) {
    $stmt->bind_param('s', $_POST['clients_id_nr']);
    $stmt->execute();
    $stmt->store_result();
    if ($stmt->num_rows > 0) {
    header("Location: statusclient2a_admin.php");
    die();
    } else 
    {
if ($stmt = $con->prepare('INSERT INTO clients (clients_initials, clients_name, clients_nickname, clients_surname, clients_id_nr, clients_profession, clients_address, clients_suburb, clients_town, clients_province, clients_tel, clients_email, clients_tel_alt, clients_address_complex, user_id) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)')) {
    $stmt->bind_param('sssssssssssssss',$_POST['clients_initials'], $_POST['clients_name'], $_POST['clients_nickname'], $_POST['clients_surname'], $_POST['clients_id_nr'], $_POST['clients_profession'], $_POST['clients_address'], $_POST['clients_suburb'], $_POST['clients_town'], $_POST['clients_province'], $_POST['clients_tel'], $_POST['clients_email'], $_POST['clients_tel_alt'], $_POST['clients_address_complex'], $_SESSION['user_id']);
    $stmt->execute();
    $GET_last_ID = mysqli_insert_id($con);
    $url = 'addvehicle_admin.php?id=' . $GET_last_ID;
        header("Location: $url");
} else {
    header("Location: statusclient3a_admin.php");
    die();
}
    }
    if ($stmt1 = $con->prepare('INSERT INTO client_license (clients_id, client_license_nr, client_license_expiry, client_license_code, user_id) VALUES (?, ?, ?, ?, ?)')) {
    $stmt1->bind_param('sssss',$GET_last_ID, $_POST['client_license_nr'], $_POST['client_license_expiry'], $_POST['client_license_code'], $_SESSION['user_id']);
    $stmt1->execute();
    $stmt1->close();
    }
    if ($stmt2 = $con->prepare('INSERT INTO client_notes (clients_id, client_notes_data, user_id) VALUES (?, ?, ?)')) {
    $stmt2->bind_param('sss',$GET_last_ID, $created, $_SESSION['user_id']);
    $created = "Client added to database";
    $stmt2->execute();
    $stmt2->close();
    }   
} else {
    header("Location: statusclient4a_admin.php");
    die();
}
$con->close();
?>