Visual pane filter messes up ranking

[BI_Nooby]

I was trying to get the top 3 of my customers using the following measure:

Rankingmeasure = IF(NOT ISBLANK([_Measure1]) ,RANKX(ALLSELECTED('Customer Attributes'[Parent_co]), [_Measure1]))

And it seems to work 

But when I introduce a visual pane filter to limit it to the top 3 it goes all weird. Very weird.

Why is this?? Only 1 other slicer active, that is slicing the customer table.

[amitchandak]

@BI_Nooby , Use TOPN

example

CALCULATE([measure],TOPN(5,all(Table[Project]),[Measure],DESC),VALUES(Table[Project]))

Learn Power BI: Dynamic TOPN using TOPN/Window and Numeric parameter: https://youtu.be/vm2mdEioQPQ

[BI_Nooby]

I know I can use TOPN. I'm trying to troubleshoot to deeper my understanding of DAX.