Scenario: A Citrix Administrator discovers that a high number of Desktop OS machines are displaying as `Unregistered.' The administrator successfully logs in to one of the affected Desktop OS machines

If the Broker service were not running on the Delivery Controllers, all Desktop OS machines on those controllers would be unregistered, not just a subset.

License Server communication issues on port 27000 would affect session launches and licensing, but would not directly cause VDA registration failures.

If the computer accounts were deleted from Active Directory, the administrator would not have been able to log in to the affected machines as a domain user.

Citrix VDA registration relies on Kerberos authentication between the VDA and the Delivery Controller, which requires that system clocks be synchronized within a 5-minute skew tolerance. A time difference between the affected Desktop OS machines and the Delivery Controllers causes Kerberos ticket validation to fail, preventing registration. This explains the partial failure pattern - machines with correct time register successfully while those with clock drift do not.