Some plugins (e.g. maven-helper-plugin) can attach arbitrary artifacts from files that are stored under different paths but use the same file name.
When the artifacts have unique maven coordinates - e.g. use the same groupId, artifactId, version, but a different classifier - Jenkins attempts to archive them based on the file name only. In this case, any archived artifact will override any previously archived artifact.
This conflict can be avoided by using the canonical name of the artifact for archiving, which will produce unique artifact files.