The configuration of a vSphere HA cluster might time out on some of the hosts added to it.
When you enable vSphere HA on an existing cluster with a large number of hosts and virtual machines, the setup of vSphere HA on some of the hosts might fail.
This failure is the result of a time out occurring before the installation of vSphere HA on the host(s) completes.
Set the vCenter Server advanced option config.vpxd.das.electionWaitTimeSec to value=240. Once this change is made, the time outs do not occur.