You KNOW the Customer or Vendor was entered in your QuickBooks file but now they are no longer appearing in the lists. How do you restore the list?
Go to your “write checks” window and select the “payee field”. When you have opened the list of Payees hit CTRL + L and the name list will open. In the lower left hand side of the screen you will see “Name” which is a drop down list. Click on “resort list” and see if that resolves your problem.
If the resort list did not work it is time to get serious. Create and restore a portable company file. It is important to understand the portable file before taking this step, a portable file only includes the financial records of your company file. See this Intuit support page for more information – Support
If your portable file is also missing customer and vendor names please visit this Intuit support page for further help- support