Sometimes the vSphere-slaves do not shutdown+revert when configured to do so.
This issue occurs sporadically, noticed this when being logged in on the slave using ssh and the slave did neither shutdown nor revert after the inspected build finished and the slave got listed as "offline".
When selecting "reconnect" in Jenkins GUI, the slave gets reconnected without being reverted to the vm snapshot as desired.
This issue occurrs sporadically, impacting different slaves on different vSphere clusters.
After manually reverting the slave vm to its snapshot, then reconnecting the slave using Jenkins GUI, everything works fine again.
when viewing the configuration page, the Jenkins logs show some NullPointerException, but this seems to be totally independent of the Exceptions occurring around the time the disconnect/revert fails to happen.