PHP FTP 间歇性无法上传文件

// 尝试 5 次
$uploaded = false;
$tries = 0;
while (!$uploaded && $tries <= 5) {
    ++$tries;
    $conn = ftp_ssl_connect($host, $port, 10) or die('FTP服务器连接失败');
    //登陆（通过用户名或者匿名登陆）
    $result = ftp_login($conn, $user, $password);
    if (!$result) {
        ftp_close($conn);
        die('ftp_login 失败');
    }

    ftp_set_option($conn, FTP_USEPASVADDRESS, false);

    // turn passive mode on
    ftp_pasv($conn, true);

    $success = ftp_put($conn, $remoteFile, $localFile, FTP_BINARY);
    if ($success) {
        $uploaded = true;
        dump("ftp upload: $success, $remoteFile, $localFile");
    } else {
        dump("ftp upload failed, tries: $tries");
    }

    ftp_close($conn);
}