Issue: host disconnected VMs grayed out state but all VMs running fine ?

Restart mgmt services via SSH(Putty) or esxi shell through DCUI and Enable ssh.

/etc/init.d/hostd restart , /etc/init.d/vpxa restart , services.sh restart Then reconnect it.

Connect host console through ILO or iDRAC go to Troubleshoot option enable ssh or esxi shell.During this process host response is very slow performance when host disconnected state you need to wait For 30 to 45 Min until change settings & try SSH.

(If Host back to Normal stage but VM's grayed out ?) Check vCenter Database is Full? Disconnect and remove Add host back to VC. If still no change you need to hard reboot host ?

Shut down grayed out  VMs If all windows servers through RDP if Linux  through ssh.

To access ESXi shell ALT+F1 and back to normal mode Alt+F2 at DCUI. Thank You.

Useful ESXCLI commands for configuring and troubleshooting ESXi:

List VMs on the ESXi server with the World ID : esxcli vm process list

Kill a VM : esxcli vm process kill –t soft -w WorldID

esxcli vm process kill --type= [soft,hard,force] --world-id= WorldNumber

Enter Maintenance: esxcli system maintenanceMode set –-enable yes
                   esxcli system maintenanceMode set –enable true
                  vim-cmd /hostsvc/maintenance_mode_enter
Exit Maintenance: esxcli system maintenanceMode set --enable no
                esxcli system maintenanceMode set –enable false

how to reboot in esxi host via SSH: reboot -f ,  halt,  shutdown

To Check if Host is in Maintenance ? 
vim-cmd /hostsvc/hostsummary | grep inMaintenanceMode vimsh -n -e /hostsvc/hostsummary | grep inMaintenanceMode 
List physical NICs and connection state : esxcli network nic list 
List network information for the VM: esxcli network vm list 
List the devices currently controlled by the VMware NMP Multipath Plugin ? 
esxcli storage nmp device list or esxcli storage nmp satp list, esxcli storage core device vaai status get. 
To Change: esxcli storage nmp satp set --default-psp=policy --satp=your_SATP_name

• VMW_PSP_MRU for Most Recently Used mode
• VMW_PSP_FIXED for Fixed mode
• VMW_PSP_RR for Round Robin mode 

• https://kb.vmware.com/s/article/2053628

Hope this will be informative for you Thanks for Reading !