Invalid content was found starting with element core-threads - xml validation broken?

Hi,

I ve tried to tune the job executor as shown in here: Performance tuning Camunda 7 | Camunda Platform 8 Docs

However when I add the three tags for threads, camunda doesn t want to start and gives the error:

cvc-complex-type.2.4.a: Invalid content was found starting with element '{"http://www.camunda.org/schema/1.0/BpmPlatform":core-threads}'

My xml file looks like this:

Any Idea? What am I doing wrong?