Sorting not working on queried subobjects.

I have following code in my expression rule, its giving the data correctly but when i apply sorting it is working fine for all the other fields but for the fields: "Headlines" and "ArticlePostDate" it shows empty data, doesn't return any data. These two are the fields that are not part of the main table and i am referencing it from another table that could be the cause that its not showing any data when I apply sorting in them. Can anyone please help what to do in this scenario.

Thanks

a!localVariables(
  local!sortField_txt: rule!EF_PlantDashboard_NewsPagingMapping(
    sortField_txt: ri!pagingInfo_pi.sort.field
  ),
  local!oDataQuery_txt: concat(
    "/Internal/Editable/ABC?editable=true&includeDeleted=true&$expand=Article($select=ArticlePostDate,Headline)&$filter=Key+eq+",
    ri!Key,
    "&$count=true&$top=",
    cons!EF_PLANTDASHBOARD_NEWS_PAGESIZE,
    "&$skip=",
    ri!pagingInfo_pi.startIndex - 1,
    "&$orderby=",
    local!sortField_txt,
    if(
      ri!pagingInfo_pi.sort.ascending,
      "+asc",
      "+desc"
    )
  ),
  local!integrationResponse_at: rule!IntOData_GetRequest(
    oDataQuery_txt: local!oDataQuery_txt
  ),
  local!isSuccess_bl: rule!OData_IsRequestSuccessful(
    integrationResponse_at: local!integrationResponse_at
  ),
  local!rawData_at: rule!OData_ExtractResponse(
    integrationResponse_at: local!integrationResponse_at,
    isSuccess_bl: local!isSuccess_bl
  ),
  local!count_int: rule!OData_GetTotalCount(
    integrationResponse_at: local!integrationResponse_at,
    isSuccess_bl: local!isSuccess_bl
  ),
  local!dataset_map: if(
    local!isSuccess_bl,
    a!forEach(
      items: local!rawData_at,
      expression: a!map(
        KeyArticles: fv!item.KeyArticles,
        KeyDoc: fv!item.KeyDoc,
        Key: fv!item.Key,
        Headline: cast(typeof("a"), index(fv!item.Article, "Headline", {})),
        ArticlePostDate: cast(typeof(now()), index(fv!item.Article, "ArticlePostDate", {})),
        UpdOperation: fv!item.UpdOperation,
        UpdOperationLabel: if(
          tointeger(fv!item.UpdOperation) = 0,
          "New",
          if(
            tointeger(fv!item.UpdOperation) = 1,
            "Updated",
            "Deleted"
          )
        ),
        UpdDate: fv!item.UpdDate,
        AppStatus: fv!item.AppStatus,
        AppStatusLabel: if(
          tointeger(fv!item.AppStatus) = 2,
          "Approved",
          "Not Approved"
        )
      )
    ),
    {}
  ),
  a!dataSubset(
    startIndex: ri!pagingInfo_pi.startIndex,
    batchSize: ri!pagingInfo_pi.batchSize,
    sort: ri!pagingInfo_pi.sort,
    totalCount: local!count_int,
    data: local!dataset_map,
    identifiers: index(local!dataset_map, "KeyArticles", {})
  )
  
)