Sessions Performance Issue (php7.1, CI 3.1.5)

I have the following code below and even in the view method, it can still get locked (With redis or database driver). I want to be able to run the view method parallel. It doesn't seem to do this all the time.

Code:

<?php
class App_files extends MY_Controller
{
    function __construct()
    {
        parent::__construct();    
    }
    
    //$extra_file_name can be used for SEO purposes but is not acutally used in function
    function view($file_id,$extra_file_name = FALSE)
    {
        //cast to index in case we have extension
        $file_id = (int)$file_id;
        //Don't allow images to cause hangups with session
        session_write_close();
        $this->load->model('Appfile');
        $file = $this->Appfile->get($file_id);
        $file_name = $file->file_name;
        $this->load->helper('file');
        header("Cache-Control: max-age=2592000");
        header('Expires: '.gmdate('D, d M Y H:i:s', strtotime('+1 month')).' GMT');
        header('Pragma: cache');
        header('Content-Disposition: inline; filename="'.$file_name.'"');
        header("Content-type: ".get_mime_by_extension($file->file_name));
        
        if (function_exists('header_remove'))
        {
          foreach(headers_list() as $header)
            {
                if (strpos($header, 'Set-Cookie') === 0)
                {
                 header_remove('Set-Cookie');
                }
            }
        }
        echo $file->file_data;
    }
}
?>