In the release notes it is stated that using the Load Balancer IP Address is not supported for Upgrading from 3.0 to 3.3. It must be done from the master node's FQDN.
VMware vRealize Log Insight 3.3 Release Notes
While in the documentation it is stated that it is supported "If using the integrated load balancer, navigate to the load balancer address, otherwise navigate to the master node address."
So which is it ?
If you actually attempt the upgrade from the ILB it will immediately force you to redirect to the master. Thanks for pointing this out, I have a doc bug open and we should have this fixed by tomorrow.
Docs have been updated!