Summarizing a second table variable doesn't work right

[yasbos]

Good day, friends! In the below code, I'm summarizing the duration per subtask. If the task has no end date, I'm calculating the duration as being the difference between the start date and today's date. 

So, the below TotTimeTask table produces a list of TaskID, SubtaskID, Duration

define var TotTimeTask= calculatetable(ADDCOLUMNS(summarize(SubtaskFact,SubtaskFact[TaskID],SubtaskFact[SubtaskID]), "SubtaskDuration"
    ,calculate(if(isblank(average(SubtaskFact[SubtaskEndedOn]))
            ,datediff(average(SubtaskFact[SubtaskStartedOn]),today() ,SECOND)  
            ,sum(SubtaskFact[durationSeconds]))
))
)
The above works fine and shows the correct results.

Here is the problem. Now, I want to summarize the above table at the TaskID only. I Do Addcolumns/Summarize again but leave out the SubTaskID. 
evaluate addcolumns(summarize(vTotTimeTask,SubtaskFact[TaskID]), "TaskDuration",calculate(SUMX(TotTimeTask,[SubtaskDuration])))

What the above gives me is the grand total in every row for TaskDuration. I don't understand why!

I can't share the file because it uses tabular direct connection.

Thanks for your help.

[amitchandak]

@yasbos , A new column with Sumx and table TotTimeTask, will sum up all the data of that table in column

Try groupby with current group

refer

https://medium.com/@amitchandak/power-bi-power-query-vs-dax-append-and-summarize-data-233f173d0839

[yasbos]

I get the below error.
function group by scalar expressions have to be aggregation functions over currentgroup(). the expression of each aggregation has to be either a constant or directly reference the columns in currentgroup()