When a shareholder exits your company (ie. sells all of their shares and other holdings) they become a former shareholder, and no longer appear on your list of current shareholders on your shareholders page.
Here are some ways that company administrators can find the details for a former or historical shareholder:
Filter your shareholders at a past date using the field 'View as on date' and click the 'Filter results' button. Select a date before the shareholder exited the company.
Find the share transactions involving any former shareholder by visiting your transaction history via the menu option for 'Share register' > 'Transaction history' and filtering for the former shareholder name.
Download your full share register. The share transactions of former shareholders are included in your share register.