After patching/upgrading vCenter, the CD/DVD on the vCenter VM in the vSphere UI continues to show the ISO as connected.
Disconnecting the ISO and using the 'Client Device' causes the vCenter to become unresponsive to pings.
ISO is locked by the vCenter guest OS
Connect directly to the ESXi host UI
The following screen will be observed
Select 'Yes' & Answer
Confirm 'Client Device' is now connected on the VM in the vSphere UI