Let's resort your customers list to get it back to the original or its default order in QuickBooks. I'll guide you how.
Click on the Customer menu and choose Customer Center.
Go to View at the top left of QuickBooks and select Re-sort List.
Select OK to confirm the action.
If the problem persists, let's run the Verify and Rebuild tool. This helps detect any issues in your company file and corrects them. Please ensure to create a backup copy and QuickBooks is updated to the latest release beforehand.
Otherwise, repair QuickBooks to refresh the program and fix any possible data damage.