OMV no longer starting

I have a bit of a curious issue with my OMV instance. It has been running rock solid for months as a VM within Proxmox but today I started having issues with it. It started because a backup job failed and that's how I found out that OMV was down.

In Proxmox, I start the VM and everything seems to go fine. I see Grub, then OMVs standard screen with the IP address and all that, indicating that it is ready to go. However, a few seconds after it starts, it'll shut down completely. I've attempted to restart it, always with the same results. All other VMs in the Proxmox host are working fine. No hardware changes were made. It seems like it starts and immediately something tells it to shut down. I don't even have time to log in to check logs or attempt to prevent the shutdown.

The VM has plenty of resources, including 24 GB of RAM, 20 cores, etc.

Has anyone had a similar issue and how was it resolved?

Major breakthrough just now. I had to film the startup sequence so that I could read the shutdown message as they're on screen for what seems one millisecond and I couldn't read it.

I read: /usr/lib/systemd/system-shutdown/nutshutdown failed with exit status 1.

This might be an important clue as this server is connected to a UPS and we did have a power outage this morning at 2:30 am. I think OMV thinks there is still backup power going to it and shuts down because of it.

The question now is how do I change this if I cannot even log into the machine since it shuts down immediately after startup.

Success.

I shut down the UPS server (UPS is attached to other hardware) and I was able to get OMV to start. I've disabled the UPS service for now and it is going strong.

Does anyone know how to fix this?

I can't tell if the server that's attached to the UPS is telling OMV that there's no power and OMV decides to shut down or of OMV's NUT is to blame and somehow it thinks there's no power.