We have been experiencing something strange and unusual the past couple of months. We get about 30 orders a day, and for the past 2 months, we have 5 known cases where customers place an order, but the order is not created in Magento. They are charged, and there is a transaction in Authorize.NET. There is a quote in Magento DB, but no order or invoice records. Authorize.Net holds what the order's "Increment ID" should be, but when you try to look it up in the backend Sales -> Orders, it is not there.
Searching on Google, I see cases of this happening when the orders are placed through eBay or some other interface, but in these cases the customers are placing orders directly the our site.
The only thing I've found that these orders have in common is they are placed roughly around the same time (authorize.net submit date), between 18:00-20:00. We do have crons for data imports and db backups, but those run around 22:00-1:00.. What could possibly be causing this? I'm hoping this isn't too local of a question, and sorry if it is.