Jenkins expects any Shared Library repository to have a src/ or a vars/ folder in its root.

However, the Plastic plugin enforces a Plastic-workspace name, and places the repository contents within a Plastic-workspace folder inside of the Jenkins-workspace folder.

Since Plastic places all files within an extra folder, Jenkins is unable to find the Shared Library source files.

This, in turn, means that Shared Libraries cannot be sourced from Plastic repositories.