Hi,
Did you do any reconfiguration of the HA or adding/removing any ESXi hosts of the Cluster?
Because that is when you do any changes on one of the ESXi hosts, the primary node in this case.
Double-check if all ESXi hosts are correctly configured with HA.
Last case, disable HA. Let vCenter remove all HA agents from ESXi hosts, wait a bit and then enable HA back again.
PS: If this is a production environment, you should do this task only after hours and if you have any critical VMs running on that Cluster, you should schedule a maintenance for this work.