Unusual SUMX behaviour

Hello, I am working on a measure that needs to sum up the number of instances where the inventory of a product goes below a specified minimum quantity. This needs to be done over multiple days and for multiple store locations. 

I have managed to do this but my measure is too slow. I am close to figuring out a faster measure that works but I need some assistance. 

The measure that works but is too slow is:

Less Than Min - Slow = 
    VAR LessThanMin =
    SUMX(
        SUMMARIZE(
            'Calendar',
            'Calendar'[Date],
            "Available", 
            COUNTROWS (
                FILTER (
                    ADDCOLUMNS (
                        CROSSJOIN (
                            VALUES ( 'Product'[Product_No] ),
                            VALUES ( 'Location'[Store Name] )
                        ),
                        "Quantity on Hand", [Quantity on Hand]
                    ),
                    [Quantity on Hand] <= [Min Qty] 
                        && NOT ( ISBLANK ( [Quantity on Hand] ) )
                )
            )
        ),
        [Available]
    )

    Return 
        LessThanMin

The measure that is faster but not quite working is:

Less Than Min - Not Working = 
    
    VAR CrossjoinTable = 
        FILTER(
            ADDCOLUMNS (
                CROSSJOIN (
                    VALUES ( 'Product'[Product_No] ),
                    VALUES ( 'Location'[Store Name] )
                ),
                "Quantity on Hand", [Quantity on Hand]
            ),
            NOT ( ISBLANK ( [Quantity on Hand] ) )
        )

    VAR LessThanMin =
        SUMX(
            SUMMARIZE(
                'Calendar',
                'Calendar'[Date],
                "Available", 
                COUNTROWS (
                    FILTER (
                        CrossjoinTable,
                        [Quantity on Hand] <= [Min Qty] 
                    )
                )
            ),
            [Available]
        )

    Return
        LessThanMin

On the image here below you can see an example of one product at one location.
The inventory goes below the minimum quantity for 15 days during the period.
You can see that the measure that is not quite working is identifying the right days but does not sum up the days (Column total is blank) 

The only difference in the two measures is that the crossjoin table has been made a variable in the second measure, which is why I don't understand why SUMX behaves in a different manner. 

Any assistance would be greatly appreciated!

Best regards, 
Arni Thor