powerbi previous time period comparison

Question

I have found on youtube a nice tutorial of how to get a dynamic time period comparison (idk if I'm allowed to put a link so just type "Previous Dynamic Period using DAX in Power BI" by radacad)

So here's the dax code:

sales_prev_period = 
var a = CALCULATE(
    SUM('MESURES'[valeur]),
        FILTER(ALL('MESURES'),
            DATEVALUE('MESURES'[date_heure]) >= DATEVALUE('prev_date_stamp'[prev_start_date])
            && DATEVALUE('MESURES'[date_heure]) <= DATEVALUE('prev_date_stamp'[prev_end_date])
        )
    )
RETURN
IF(a > 1000000000, CONCATENATE(FORMAT(a, "######,##,,,.0G"), "Wh"), 
    IF(a > 1000000, CONCATENATE(FORMAT(a, "######,##,,.0M"), "Wh"),
        IF(a > 1000, CONCATENATE(FORMAT(a, "######,##,.0k"), "Wh"),
                      CONCATENATE(FORMAT(a, "###0.0"), "Wh"))
    )
)

This part returns me always Null / Empty

In contrary this bit of code just under (which is the same but with the "current" dates) always returns me the sum of all values (like if the filter wasn't applyed)

sales_current_period = 
var a = CALCULATE(
    SUM('MESURES'[valeur]),
        FILTER(ALL('MESURES'),
            DATEVALUE('MESURES'[date_heure]) >= DATEVALUE('prev_date_stamp'[start_date])
            && DATEVALUE('MESURES'[date_heure]) <= DATEVALUE('prev_date_stamp'[end_date])
        )
    )
RETURN 
IF(a > 1000000000, CONCATENATE(FORMAT(a, "######,##,,,.0G"), "Wh"), 
    IF(a > 1000000, CONCATENATE(FORMAT(a, "######,##,,.0M"), "Wh"),
        IF(a > 1000, CONCATENATE(FORMAT(a, "######,##,.0k"), "Wh"),
                      CONCATENATE(FORMAT(a, "####"), "Wh"))
    )
)

Any idea where it can come from? how to solve it?

Thanks!