It appears that when the workspace is cleaned by Jenkins after/before use, the targets of symlinks are deleted, but the symlinks themselves are not.
We now have most workspaces containing dead symlinks - some of which were checked out of the Perforce repository, and some created during the build process (when they had valid targets). None of the symlinks point outside of the workspace - most (all?) are to another file/directory in the same parent directory.
These builds are driven by Jenkinsfiles as DSL pipeline scripts.
Explict error – build failure due to Archive trying to fingerprint a broken symlink.