A Measure That Ignores Page Level Filters

i can be very wrong, but i believe that this 

Measure = CALCULATE(AVERAGE(CustomerData[Score]),
FILTER(ALL(CustomerData), CustomerData[ProductLine] = "xxx"),
FILTER(ALL(CustomerData), CustomerData[Tenure] > 123))

actually doesnt do what you expect it to do, the second filter is actually overwriting the first one,

you should try this:

Measure = CALCULATE(
                  AVERAGE(CustomerData[Score]),
                  FILTER(ALL(CustomerData), 
                                     CustomerData[ProductLine] = "xxx" 
                                      && CustomerData[Tenure] > 123)
)

also, the ALL filter will ignore all filter outside the CALCULTE context, so is highly improbable that what is bugging your calculation is the page level filter; try fixing the measure as above and if you can help us with some context, example, demo, anything more material.

;)