I have an issue with the customer Group NOT LOGGED IN.
When a customer buys a product, without register himself on our website, the customer will normally added to customer group NOT LOGGED IN.
At my website, this does not work. The customer is not added to any customer group. I have to add the customer group manually in the database at sales_orders and sales_orders grid. See the attachment.
When I change it to "0", the customer get the customer group NOT LOGGED IN in the backend of the order.
I have no issues when a customer registers himself at my website.