Visual and dax level optimization that causes report slowdown

Since in matrix you use months only as periods, changed  grouping a bit. To the Data table column is added

Month = RELATED( 'Calendar'[Month] )

and new measures are

Count of Exisitng Days by Month = VAR bydates =
    SUMMARIZECOLUMNS (
        Data[Month],
        "count",
            COUNTROWS (
                DISTINCT ( SELECTCOLUMNS ( Data, Data[Date], Data[DBName-Point_Id] ) )
            )
    )
RETURN
    SUMX ( bydates, [count] )

///
Data Completeness by Month = DIVIDE ( [Count of Exisitng Days by Month], [Count of Possible Days] )

With them matrix calculation is

compare to

Not a lot but at least something. Matrix is on "Page 1" at PR-419 - Data Coverage - 03.pbix