When you attempt to migrate an NSD tunnel to a new GCP gateway, the migration will fail with an error message that states, "Not a valid IP address".
There is a potential issue with the assigned IPv6 value within the VCO database for the GCP gateway. Proceed with opening a case with Broadcom support with the details on the NSD migration that is failing, and the GCP gateway you are unable to migrate too. Share with support this article as well.