Current issues in ZCS 8.6
Current (Known) Issues in ZCS 8.6 Build 1153
Upgrading from 8.5.1 to 8.6 doesn't check the local proxy variables and it fails the upgrade. When upgrading, the Script validates the license against https://license.zimbra.com. If your Server is behind a proxy the upgrade script (and also the license activation itself) ignores the Proxy System Variable.