During a cluster upgrade, the list of hosts to upgrade comes from different sources. This is important to remember when looking into failed upgrades or other unexpected upgrade issues.
In addition to the host list in the Cluster Manager database, one of two files exist on the Cluster Manager machine, c:/ec_nodelist and/or c:/ec_nodelist_mega (Windows) or /var/tmp/ec_nodelist (Unix). These files are the sum of all hosts known to the cluster and act as a backup to the upgrade process.
If hosts are moved manually, this list can become out of sync with the actual cluster. Before upgrading, you can remove these files from the Cluster Manager machine and the upgrade will not be attempted on those extra machines.