You have a customer who comes regularly for ages and now for some reason you never see them. This is a common problem in business and here is a way of detecting who they are.
Go to main menu and click on "Customer Reports" as shown by the green arrow.
Now go to "Customer accounts" and then go "Non-Active Accounts" as shown with the blue arrow.
Now just go into the basic section in criteria and this will pop up.
I have put here a request to get a listing of all customers that have not traded with you for six months. You can, of course, select any period you wish.
Now off will pop out a list of all those customers who no longer trade with you for you to investigate.