You mean it processed as an empty cart and only had the shipping charge?
What is the web site url? Is it possible that they had used http://www.yoursite.com or http://yoursite.com and only one or the other works? The inclusion or omission of the www. in the url could cause that issue if when you redirect to the https:// version of the page it uses the opposite.
The solution is to force www. or remove the www. for consistency using the .htaccess file (if that is indeed the issue).