Mahmoodul This looks like a measure totals problem. Very common. See my post about it here: https://community.powerbi.com/t5/DAX-Commands-and-Tips/Dealing-with-Measure-Totals/td-p/63376

Also, this Quick Measure, Measure Totals, The Final Word should get you what you need:
https://community.powerbi.com/t5/Quick-Measures-Gallery/Measure-Totals-The-Final-Word/m-p/547907

Mahmoodul , distinct count can vary in total as it grand total is calculated again

You can Try like

sumx(values(table[SCS_NAME]), DistinctCount(Table[Prime Part]))

sumx(summarize(table, table[SCS_NAME], Table[Age Bucket],"_1", DistinctCount(Table[Prime Part])),[_1])

Hi, Mahmoodul 

I'd like to suggest you try the following measure to see if it helps.

Result =
IF (
    NOT ( ISFILTERED ( Table[SCS_NAME] ) )
        && NOT ( ISFILTERED ( Table[Prime Part] ) ),
    SUMX ( VALUES ( Table[SCS_NAME] ), DISTINCTCOUNT ( Table[Prime Part] ) ),
    DISTINCTCOUNT ( Table[Prime Part] )
)

Best Regards

Allan

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.