Unless you have enabled sessions statistics by mistake via the PT-icon (HUD will have a red background) or are
using HUD filters then lifetime statistics should be displayed however if you have only just started using PokerTracker 4 and have a small database then bear in mind you will not have many hands on your opponents yet and since PokerStars is one of the biggest sites you will not necessarily be seeing the same players all of the time.
Also if you've played with players before in other sessions was this before you started using PokerTracker 4? In that case PokerTracker 4 wouldn't know about those hands unless you have manuallu imported them from where you had them saved but PokerStars can provide you with copies if required. You can also check the lifetime statistics for all players in your database by creating an 'All Players' report in 'My Reports:
Guide: Creating My ReportsIf the data there isn't matching the HUD (without filters) then send us a screenshot and your log file in a
Support Ticket:
Tutorial: Reporting A Problem