We're not able to claim unstable builds any more (with declarative pipeline). For failed builds, it still works. I'm pretty sure it worked for unstable builds as well so I guess this is a regression.

The plugin is called in post section, independant of build result:

post {
  always {
    step([$class: 'ClaimPublisher'])
  }
} 

 We're currently using:

• Jenkins 2.138.3
• Claim Plugin 2.15