@JeremyL Hi, yes I am sure I have run Fog under Proxmox as well successfully but this time it didn’t want to work. Anyway once I switched to using Fog running under a Container, it uses much fewer resources and runs just as well.
So I would recommend switching to running it under a container when possible.

Hi all,
To anyone with the same issue,
this was caused by running Fog on a virtual machine under Proxmox.
To run under Proxmox - it needs to be installed as a Privileged Container with nesting and NFS enabled under the options.
It will then work.
The issue is to do with the NFS sharing, I think that perhaps a port or something is blocked and the above approach gets around it.