When running the build the actions performed by the Copy Artifact plugin are not being logged in the Console.
There should be indication in he Console of what artifacts are being copied from which job and to which directory, before action is actually performed. As it is when builds fail because required artifacts that were to be copied from other jobs are hard to trace because there is no indication that was the reason the build failed.
Since no information is shown the culprit is the previous log entry that have no relation to the real problem.
Please be more verbose with the Tasks performed with this plugin in Console.