we resolved this by removing hosts, restart all the agents on the hosts with "services.sh restart"
we also deleted a giant log file in /tmp before upon agents restart, we couldn't connect directly to the host
once we deleted the big log "mili....log" we restarted the services properly again and then we re-added the hosts.
We couldn't reboot as vcenter 6.5 appliance is running on one of them and vmkernel for migration wasn't available.
Once we re-added the esxi host in vcenter, we were able to see adapter, but they didn't have VDS assigned
we re-assigned the vmnic to the dvuplink in the VDS (adding.managing hosts), they needed to re-assigned to the dvuplinks
once assigned we migrated the vmkernel into the mgmt vlan
it seems now it found HA heartbeat again, but the VMs didn't show inside the VDS, we found out "editing" each VM, without touching anything, clicking ok, was putting them back into the VDS
We did all of this via the HTML5 portal of vcetner 6.5 (and of course ESX shell on the hosts).