I am calling these functions

zip(zipFile: "it-surefire-its-${stageKey}.zip", dir: 'surefire-its/target', archive: true)

archiveArtifacts(artifacts: '*.zip', allowEmptyArchive: true, onlyIfSuccessful: false)

When the build fails, the artifacts are not available for downloads.

If is succeeds, they are available.

This is the script https://github.com/apache/maven-surefire/blob/master/Jenkinsfile

And you can try out this job for instance:

https://builds.apache.org/job/maven-wip/job/maven-surefire/job/SUREFIRE-1495/

I use function parallel() as well. Could it be the case?

If I use similar script in my company without parallel(), the artifacts can be always downloaded.