That stat is in the Holdem Cash Session
s section, which is used in reports which display totals over multiple sessions.
The Sessions tab displays individual sessions and stats used there are in the Holdem Cash Session (singular) section.
If you want to display the rakeback stat there you will need to build a version of it in the Holdem Cash Session section.
This probably just consists of copying the column expression to the new section and removing the SUM( ) from the expression (becuase it will then be calculating the value for a single session rather than summing the total across all sections).
See the
Tutorial: Custom Reports and Statistics for an explanation of the stat sections.
If you need help converting the stat to the new section please export and attach it to a
Support ticket and we'll help you out.