When the server is rebooted, some VMs got failed to boot with systemd/dbus error messages. 

Rebooting the affected VMs resolves this issue.

Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to NameOwnerChanged signal for 'org.freedesktop.DisplayManager': Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to NameOwnerChanged signal for 'org.freedesktop.NetworkManager': Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to NameOwnerChanged signal for 'org.freedesktop.login1': Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to NameOwnerChanged signal for 'org.freedesktop.Accounts': Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to NameOwnerChanged signal for 'org.freedesktop.Avahi': Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to NameOwnerChanged signal for 'org.freedesktop.ModemManager1': Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to subscribe to activation signal: Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to register name: Connection timed out
Jan 30 20:40:02 VM systemd[1]: Failed to set up API bus: Connection timed out

an 30 20:40:32 VM dbus[1009]: [system] Failed to activate service 'org.freedesktop.systemd1': timed out
Jan 30 20:40:32 VM systemd-logind[998]: Failed to enable subscription: Failed to activate service 'org.freedesktop.systemd1': timed out
Jan 30 20:40:32 VM systemd-logind[998]: Failed to fully start up daemon: Connection timed out

Host machine specifications:-

OS        : Ubuntu 16.04

Kernel  : 4.15.0-47-generic 

CPUs   : 48 ( 2*12*2)

RAM    : 64G

VM specifications:-

Kernel  : 4.13.16

CPUs   : 8

RAM    : 4G

Attached the full log file.

Kindly help us to resolve this issue with a permanent fix.