Customer purchase without any records...

Apparently a purchase was made on one of our opencart stores, however there is absolutely no record of the customer or the purchase in opencart. But the payment was received through Auth.net.

Anyone have any idea what might be going on?

Go in admin to sales > orders and filter the orders by "missing orders", if there you can find the order to match the amount and payment method then something mightve went wrong with the verification of the payment, also check your error log for any errors related to payment.

Ok, so I see that the person placed 2 orders and they are located in the "Missed Orders" section. However, from what I've read, Missed Orders generally pertain to orders that were abandoned, IE the customer did not hit the confirm order button.

But how would that explain the payment still going through Auth.Net?

Thanks for directing me to the Missed Orders area.

We get this some times with Paypal - somewhere along the line the 'this went through' messes up.

As above you might find info in your logs, I've never been successful on that front though.

Best bet is to keep a close eye on your auth.net account, easy to spot orders that don't tally

As Tony said Paypal also fails sometime to send a response that the order has been paid and the order goes to missing order, this could be the case, if it continues to happen for all orders then they migtve updated something and the payment module needs update too otherwise if its isolated I doubt there is something you can do to prevent it.