Customers not added to Customer list - Version 1.4.9.1

I have an OpenCart install that has been going great for a few years but now customers are not being added to the customer list after their order goes through. I can't think of any changes that I've made recently that would cause anything like this and I haven't upgraded the system recently so I'm at a bit of a loss. The orders are still going through, and I can see all the customer information in the order view, just not in my customer list. Any ideas as to what to check that might cause this?

So I found the problem. The client had checked a box to allow guest checkouts, which obviously would allow someone to place an order without adding themselves as a customer. Toggled a switch and we're off to the races again