VDAs become unregistered at random throughout the day, VDAs can re-register on their own but sometimes require a manual reboot. 

1. Run the Cloud Connector Connectivity Check Utility on all the Cloud connectors and check for any blockages on the required URLs. 
   • All the required URLs for the Citrix DaaS are mentioned at https://docs.citrix.com/en-us/citrix-cloud/overview/requirements/internet-connectivity-requirements.html

Problem Cause

• Most of the registration failures occurred when the below URLs are blocked access to from the cloud connectors
  • https://*.cloud.com
  • https://*.citrixdata.com
  • https://*.xendesktop.net