The Group (group tree) is based on a "PriorityGrouping" formula:
     IF {CnPrProp_1AttrCat_4.CnPrProp_1AttrCat_4_Description} in ["Med","Medium"] then
       "Medium"
     else
       {CnPrProp_1AttrCat_4.CnPrProp_1AttrCat_4_Description}

This "PriorityGrouping" formula was referencing an old field and needed to be updated to refer to the new field as follows:
     IF {CnPrProp_1AttrCat_5.CnPrProp_1AttrCat_5_Description} in ["Med","Medium"] then
       "Medium"
     else
       {CnPrProp_1AttrCat_5.CnPrProp_1AttrCat_5_Description}