Sessions tab or Reports tab? If it's the Reports tab, what Report is selected? If it is the Sessions tab you are looking at, change the Group by: drop-down option to Sessions (by table).
HM starts a new 'Session' only after you haven't played a hand for 30 minutes. If you want to change the session timeout:
Close HM
C:\Program Files\RVG Software\Holdem Manager\Config\HoldemManger.config
Open with > Notepad
Approximately at line 60:
PHP Code:
<setting name="SessionTimeoutDuration">30</setting>
30 minutes of no playing = new session
I use 5 minutes
PHP Code:
<setting name="SessionTimeoutDuration">5</setting>