First, you have a typo in the post:

FILTER SUM(CASE WHEN (LEFT("COEP"."KSTAR", 1) IN ('6','9')) THEN "COEP".."WTGBTR" ELSE NULL END) != 0

you have 2 dots, not one.

Apart of that, one reason of not working is when there is no relationship in the model between the columns in the filter and one or several of the columns used in the component

HTH

Correctly. The point is too much.

to your second point. The formula works as a KPI, which means that the columns are connected in my opinion.

Only inserted in the component filter, I have the problem and also the following error analysis...

"An aggregation is not a function. Please check that there are no dimensions and aggregations used together as a function inputs"

Well, it is not the same that a formula will work as dimension/kpi or as a Filter component. At least in my experience.

the trick is to put in a OLAP table the KPI, and the dimensions/values you want to filter. If it shows values then should be ok

But, regarding the error message... yes your KPI is an aggregation, so I found that, depending the specific case, it will not work (as it tries to apply the filter to each instance of the dimension)

Not sure if I explain myself...

HTH