Follow all configuration settings as described in this link:  https://plugins.jenkins.io/atlassian-bitbucket-server-integration/

Push / PR, not fire freestyle job although it did work for a multibranch pipeline job ( not at the same time ).

Changing from "Bitbucket Server" in SCM into "Git" did fire a job after Push / PR in Bitbucket.

Plugin Version: Bitbucket Server Integration 3.3.2

Steps :

1. Configure Job as a descript here: https://plugins.jenkins.io/atlassian-bitbucket-server-integration/#plugin-content-select-a-bitbucket-server-instance-when-creating-a-freestyle-job
2. Verify webbook is created ( see images below )
3. Create PR 
4. Freestyle Job should start to  build with 

5. Triggered by Bitbucket webhook due to changes by Danil Shalumov.
   Running as SYSTEM