会话变量维护一些但不是简单购物车的所有用户

I have a php site I wrote that stores some information retrieved from forms for eventual input into backend as session variables. Here are the simple steps for each 'transaction':

1. Users fill out form
2. data is stored in session variables (some session arrays)
3. users click 'pay now' and head to bank to pay
4. if bank returns 'approved' data is written to tables.

Here is the problem: it works for me every time on my development site which is a copy of the live site. It works only some of the time for users of live site.

Here are some ideas I have:

1. a SSL certificate was added
2. the session settings in phpInfo could be wrong/maxlifetime is 1440??
3. maybe a problem for some browsers coming back from bank...their https to our new https

Session config :

session.auto_start  Off Off
session.cache_expire    180 180
session.cache_limiter   nocache nocache
session.cookie_domain   no value    no value
session.cookie_httponly Off Off
session.cookie_lifetime 0   0
session.cookie_path /   /
session.cookie_secure   Off Off
session.entropy_file    no value    no value
session.entropy_length  0   0
session.gc_divisor  100 100
session.gc_maxlifetime  1440    1440
session.gc_probability  1   1
session.hash_bits_per_character 4   4
session.hash_function   0   0
session.name    PHPSESSID   PHPSESSID
session.referer_check   no value    no value
session.save_handler    files   files
session.save_path   /tmp    /tmp
session.serialize_handler   php php
session.upload_progress.cleanup On  On
session.upload_progress.enabled On  On
session.upload_progress.freq    1%  1%
session.upload_progress.min_freq    1   1
session.upload_progress.name    PHP_SESSION_UPLOAD_PROGRESS PHP_SESSION_UPLOAD_PROGRESS
session.upload_progress.prefix  upload_progress_    upload_progress_
session.use_cookies On  On
session.use_only_cookies    On  On
session.use_strict_mode Off Off
session.use_trans_sid   0   0

I'm at a loss as I cannot replicate this issue. I know transactions are taking place as they are present 'on the bank side'...just no data being written to our backend tables indicating a break when users are sent back to the website to my file that writes the data (please see an abbreviated version below)

<?php
session_start();
include('lib/phpmailer/PHPMailerAutoload.php');
require_once('functions.php');
require_once('db/configdb.php');
$amount = $_POST['x_amount'];
$authCode = $_POST['x_auth_code'];
$bank_email = $_POST['x_email'];
$bank_name = $_POST['CardHoldersName'];
$responseCode = $_POST['Bank_Resp_Code'];
$responseMessage = $_POST['Bank_Message'];
if(isset($_SESSION['cart'][0]['description'])){
    $description = $_SESSION['cart'][0]['description'];
} else {
    $description = $_SESSION['description'];
}
$item = $_SESSION['cart'][0]['item'];
$firstName = $_SESSION['firstName'];
$lastName = $_SESSION['lastName'];
$address1 = $_SESSION['address1'];
$address2 = $_SESSION['address2'];
$city = $_SESSION['city'];
$zip = $_SESSION['zip'];
$state = $_SESSION['state'];
$email = $_SESSION['email'];
if($responseMessage!="Approved"){
    $sessionKey = "username";
    foreach($_SESSION as $key => $value){
      if($key == $sessionKey) continue;
      unset($_SESSION[$key]);
    } 
    header("location:payment-issue.php?reason=".$responseMessage."");
    exit();
} else {
    switch ($item) {
        case $item=="train":
            $reason = "train";
            $sqlUpdate = $db->query("INSERT INTO payments (data) VALUES (data)");
            $sqlTrain = $db->query("INSERT INTO training (data) VALUES (data)");
            break;
        case $item=="renew":
            $reason = "renew";
            $sqlUpdate = $db->query("INSERT INTO payments (data) VALUES (data)");
            break;
        case $item=="donate":
            $reason = "donate";
            $sqlUpdate = $db->query("INSERT INTO payments (data) VALUES (data)");
            break;
        case $item=="new member":
            $reason = "new member";
            $sqlAdd = $db->query("INSERT INTO newMembers (data) VALUES (data)");
            $sqlUpdate = $db->query("INSERT INTO payments (data) VALUES (data)");
            break;
        default:
            $sqlUpdate = $db->query("INSERT INTO payments (data) VALUES (data)");
            break;
    }
}
$sessionKey = "username";
foreach($_SESSION as $key => $value){
  if($key == $sessionKey) continue;
  unset($_SESSION[$key]);
} 
die(header("location:thank-you.php?reason=$reason"));
?>