After you upgrade your VCenter to 6.5, you’re stuck at loading screen after you login.
This happens because the user you are logging in does not have the proper permission. To fix the issue, try logging in as user email@example.com (using the credential you used for setting up the single sign on).
Once you’re logged in as firstname.lastname@example.org, add the problematic user to proper group, so you can login and manage the VM.
From Home, go to Administration.
Under the Administration menu, go to Single Sign-On, and select Users and Groups. Chooose the user you want to assign permissions to.
Then you give the user the proper Assigned Role that you need.