Firstnonblank is not working right

Hi everyone.

The structure I have is pretty complex and maybe that's the reason why the formula doesn't work right.

So, I have a calculated table 'Customers calc'. It is mainly based on NATURALLEFTOUTERJOIN(customers,subscriptions). This table has a service_code column by which I'm trying to get a case_study_link from another table. Since one service_code can have multiple case_study_links, I'm using FIRSTNONBLANK.

The calculated column is the following:

Case study = 

CALCULATE (

FIRSTNONBLANK( case_studies[case_study_link], 1 ),

FILTER ( ALL ( case_studies ), case_studies[service_code] = 'Customers calc'[service_code] ))

 

And it does return a right case_study_link in 32 cases, while I have more than 100 values. So in some cases, it returns blank instead of the value, while in others it works fine. I don't see any regularity here...

 

I'm attaching a screenshot of the model with the abovementioned tables.

I would appreciate any help.