CentOS Not Booting

Apr 2021
aka Centos Emergency Mode.

This has been listed under IPHE, not because it is specific to IPHE (because it is not) but because it was on an IPHE system that I first observed this phenomenon.
After a server was rebooted (and I cannot say whether this was a reboot from a command line, a server crash, someone pulling out the power cables, a power cut etc) the end result is that the server will not fully boot up, instead we end up in 'emergency mode'.
When logging in to the server from command KVM or from BMC (or whatever remote management is present) we can see the following tell tale screen: