Where you see recent activity on a contact’s front page – this is only a preview and works when you are viewing the record on the main contacts screen (before you click into the record itself) – please see screenshot below to show a preview pane of ‘recent activity’ when the mouse is on a contact’s record.
If there is no History activity recorded inside the record you will not see this on the ‘preview’ but only Notes (if recorded).
Once the record is opened the default page is the Custom Fields section.