1. Disable firewall and check host connect back in vcenter.
# esxcli network firewall get
# esxcli network firewall set --enable false
2. If host connected back in vcenter after disabling firewall , then re-enable firewall again and monitor host.
# esxcli network firewall set --enabled true
3. if host disconnected in vcenter again , enable "VMware vCenter Agent"
Go to Host through vClient >> Select Configuration >> Go to "Security Profile" >>> click on "Edit" >> Click Check-mark on box "VMware vCenter Agent" for Port 902.
Check now host will connect back in vcenter