Which nodes don't have complete unicast lists: the first node or any additional nodes? Any set to ignore vCenter unicast updates?
As you didn't create the cluster through vCenter, if there is no data on this cluster (e.g. it is new and blank) then probably best to create a new cluster with the new nodes, migrate the vC to it and then move the first bootstrapped host.
Alternatively unicast agent lists are simple to rebuild (VMware Knowledge Base ) but it is best to ensure that vCenter knows the cluster as well as the nodes do, e.g. vCenter is authoritative in vSAN Health should be green and all nodes with the same information as the vCenter.