CentOS VM not booting but entering into Emergency mode

We have a 4 months-old Opennebula setup and no issues so far. A CentOS VM (which was running without issues) enters into the emergency mode after reboots. Unfortunately, we do not have any other CentOS VM running in the same environment for the comparison.

Opennebula version: OpenNebula 5.6.1
Hypervisor: KVM
OS: Ubuntu 18.04

The VM states are showed running and CentOS image parameters are the same as other images. This is the first time we encountered this kind of problem.

Please share your thoughts on this issue.