Hi Kelsey,
Where is the Subreport placed?
Could you drag and drop the {?Pm-@ShowValuesYield } parameter field on the report > right-click and check 'Can Grow'.
Does it contain all the values or any values at all?
Would you be able to attach the report with saved data?
To attach the report change its extension from .rpt to .txt and click on the 'Use advanced editor' option in the reply window.
P.S: Make sure the Main Report and Subreport are returning the same number of groups.
-Abhilash