Issue

Changes made to an agent’s configuration are not persisted in its config.xml

Environment

CloudBees Jenkins Enterprise

Resolution

You will need to manually edit the agent’s config.xml file to remove the
temporary offline lines:

<temporaryOfflineCause class="hudson.slaves.OfflineCause$UserCause">
  <description>
    <holder>
      <owner>hudson.slaves.Messages</owner>
    </holder><key>SlaveComputer.DisconnectedBy
    </key>
    <args>
      <string>anonymous</string>
      <string/>
    </args>
  </description>
</temporaryOfflineCause>