How do I activate or deactivate the upgrade in a cluster where some master candidate hosts are unavailable?

As long as any of the master candidate hosts are unavailable, activation or deactivation will not proceed. It is important that all master candidates take part in the activity to ensure the cluster will work correctly. Try to resolve the issue to make the master candidate available to the cluster, however, if it cannot be made available, it is recommended to remove it from the cluster before activating or deactivating the upgrade.