Log completely out of Sphere, clear your cache and cookies and close all windows of the browser you are working in. Reopen the browser and log back into Sphere to navigate back to Contacts > Database Management > Manage Contacts > Duplicate Checker. At times, this can force the update to the checker to complete.

Note: It can take up to 24 hours for the Duplicate Checker to complete, depending on the level of activity on the server. If it has been over 24 hours and the Checker is still showing processing or waiting to be processed, Chat With Support and reference this article.