USERELATIONSHIP & Convert BLANKS to 0

You have a couple of options. My preference is COALESCE but you can also add 0 to a measure that you supsect might return BLANK()

One slightly unrelated note: 

IF (HASONEVALUE ( Dim_Date[SLUSAWeekNum] ),
        SUMX (
            FILTER (
                ALL ( Dim_Date ),
                Dim_Date[SLUSAWeekNum] = CurrentWeek && Dim_Date[SLUSAYearNum] = CurrentYear),
            [Order Count Dispatch User]),
        BLANK ())

doesn't really need the "Else" statement as BLANK is implied.