Codeigniter Flash数据不工作1 / 10的时间

我面临一个非常奇怪的问题，Codeigniter的flash数据10次中有1次不可用。大多数时候它是有效的，但随机地它不会。所以，有人可以帮我知道这可能是什么原因。

控制器代码

public function set_pagelist(){
    $site_id = $this->input->get('site_id');
    $use_list = $this->input->get('use_list');
    if($use_list=="1"){
        $use_list = (int) $use_list;
    }
    $data = array("site_id" => $site_id,"page_list_option" => $use_list);
    $url_send = $this->api_url."set_pagelist_option";
    $str_data = json_encode($data);
    $request = sendPostData($url_send, $str_data);
    $response = json_decode($request, true);
    $errors = $response['errors'];
    $response_message = $response['response_message'];
    if (isset($response_message) && isset($errors)) {
        if (trim($response_message) === "Value Set" && trim($errors) === "None") {
            $this->session->set_flashdata('upload_message', '<p><div class="alert-box success"><span>success: </span>Value has been set successfully</div></p>');
            redirect("manage-domain");
        } elseif($response_message === "Error" && $errors === "Invalid Pagelist Option") {
            $this->session->set_flashdata('upload_message', '<p><div class="alert-box error"><span>Error: </span>Invalid Pagelist Option</div></p>');
            redirect("manage-domain");
        }
    } else {
        $this->session->set_flashdata('upload_message', '<p><div class="alert-box error"><span>Error: </span>OOPS some error occurred</div></p>');
        redirect("manage-domain");
    }
}

echo $this->session->flashdata('upload_message');