Date accumulated sum measure is running down in the last three months of the period

[Anonymous]

I have a measure calculating running total for defined period (separate calendar table was added).
Everithing seems to work fine, but for some reason it just drops in the last 3 months of the mentioned period - reflecting only very little portion of the whole dataset.
So, this is the fomula:

QualifCummulTD = CALCULATE(Sum('cpb_ mainQualificationDataSet'[QualifWeight2Col]),
    FILTER(ALL('Calendar'[Date]) ,
        'Calendar'[Date] <= Max('Calendar'[Date])
    )
)

Calendar contains all dates from mainQualificationDataSet (2005 till 2019.12)
And this is the chart output:

 

[kentyler]

QualifCummulTD =
VAR cal_date = MAX('calendar'[date])

CALCULATE(Sum('cpb_ mainQualificationDataSet'[QualifWeight2Col]),
    FILTER(ALL('Calendar'[Date]) ,
        'Calendar'[Date] <= cal_date)
    )
RETURN cal_date
)
Use a VAR to get an intermediate value.

Then return the VAR instead of the sum, so see if you can see any unexpected values in those months.