specific php session variables lost in Chrome only, - php

Question

I lose some session variables in Chrome only
After reading every similar question and answer on this site, I have to note:
It is not a 404 / missing favicon issue
Also not a redirect issue. The session is started and closed properly.
I have a $_SESSION['customer'] and $_SESSION['order'] variable, for instance.
As expected, $_SESSION['customer'] holds an object of customer data, $_SESSION['order'] holds an array of products.
When I add a product to the order, I need to look up any customer discounts for this specific product. Then it turns out in Chrome, the $_SESSION['customer'] variable is missing, and the sql query returns no discounts, since there is no customer number.
Let's give you some code to work with:
I am on the update order page, where I still have my customer and order variable.
I call this function with an ajax request to return a list of products:
public function live_search_product(){
$this->load->model('orders', 'orders');
$qry = $_GET['qry'];
if (strlen($qry)>0) {
$products = $this->orders_model->search_products($qry, false);
if ($products){
foreach ($products as $product){
echo ''.$product['short_title'] . '<br>';
}
}
}
}
I select the product from the dropdown list, and end up in this function, where I suddenly have lost my $_SESSION['customer'] object and $_SESSION['order'] array. Please note that all my other session variables still exist.
public function add_product() {
$this->load->model('orders', 'orders');
$product = $this->orders_model->get_product_by_id($this->router->id);
$discount = $this->discount->get_discount($product->id, $product->product_group_id, $_SESSION['customer']->id, $_SESSION['customer']->group_id );
$_SESSION['order'][$this->router->id] = array('product' => $product ,
'quantity' => 1,
'rental' => 0,
'bruto' => $product->price_ex,
'discount' => $discount->discount_percentage,
'netto' => ((100 - $discount->discount_percentage)/100) * $product->price_ex,
'total' => ((100 - $discount->discount_percentage)/100) * $product->price_ex);
$this->calculate_order_totals();
}
In firefox and iexplorer and edge there is no problem, it works.
I really hope you have any other suggestions.
**** EDIT ****
Every controller has an index function that is called automatically. route orders/orders will call orders/orders/index, and for instance route orders/orders/add_product, will call the function add_product in the orders controller (residing in the orders folder).
It turns out that in Chrome, somehow I get routed to the index function of this orders controller. Which is an overview orders function where I reset all order variables, to make sure nothing is left when I open a new order.
I have changed that, so this specific situation is solved.
However, can not understand why I get redirected to this function, when calling the add_product function directly.
Any ideas?