I've seen this on multiple clients on quite a wide variety of versions.
The symptoms are that an order will come through with sometimes no customer info at all or sometimes with just an email address or other snippet of info. The payment processing usually (but not always) fails with incomplete info.
The issue is random and I've tried to work with the helpdesk in the past but usually get the “can't recreate in the standard cs-cart” response.
Occasionally there is a link like the user_id that will get to the profile data and it can be resurrected. But usually there's basically nothing so the customer is done and the merchant has no idea who to contact to get it addressed.
Are others seeing this issue? As I've said, I've seen it on several clients. If it were one, I would write it off to something specific to that site. But I've seen it on at least 3 different stores all at different versions.