can you confirm if you have different server SSO? if you have external server for SSO than first you have to upgrade your SSO server as per best practice .
When you upgrade or migrate a deployment with multiple vCenter Server instances, the upgrade or migration order matters.
You upgrade or migrate externally deployed vCenter Single Sign-On 5.5 instances or Platform Services Controller 6.0 instances first. You temporarily leave the vCenter Server instances at version 5.5 or version 6.0 while you complete the upgrade or migration process for the vCenter Single Sign-On 5.5 instances or Platform Services Controller 6.0 instances.
You must upgrade or migrate your vCenter Single Sign-On 5.5 instances or Platform Services Controller 6.0 instances sequentially.
For a mixed-platform installation with vCenter Single Sign-On 5.5 instances or Platform Services Controller 6.0 instances on Windows and vCenter Server Appliance instances, upgrade or migrate all the vCenter Single Sign-On 5.5 instances or Platform Services Controller 6.0 instances on Windows before upgrading any vCenter Server Appliance instances.
For a mixed-platform installation with vCenter Single Sign-On 5.5 appliances or Platform Services Controller 6.0 appliances and vCenter Server instances on Windows, upgrade all the vCenter Single Sign-On 5.5 appliances or Platform Services Controller 6.0 appliances before upgrading or migrating any vCenter Server instances on Windows.
After upgrading or migrating your vCenter Single Sign-On 5.5 instances or Platform Services Controller 6.0 instances, you can upgrade vCenter Server instances. vCenter Server instances that point to the same Platform Services Controller can be upgraded or migrated concurrently.
Upgrade or Migration Order and Mixed-Version Transitional Behavior for Multiple vCenter Server Insta...
