It can be disconcerting to look at the View Orders page, and see missing orders. However, rest assured that this is quite normal.
Any time a customer visits the checkout page, the site creates a new order for them. If they do not pay for their order and/or abandon their cart – the site still records their order.
As an administrator, you typically only see “Active Orders” (those that have been paid for). But if you would like to see “All Orders”, look for this drop-down menu on top of the View Orders page: