Can't help with your issue, but wanted to point out that the article you linked only references Xenserver 6.X, so may not be applicable to newer versions.
When I issue the shutdown command to the host / physical machine via xoa, the process does not occur. it gives an error.
no hosts availeble
Looks like this documented issue: https://xcp-ng.org/docs/troubleshooting.html#ubuntu-18-04-boot-issue (found by looking up "ubuntu" in the docs)
During VM export, the ssh connection is gone and the result is frustrating. the disk of the virtual computer does not appear at all.
Xcp-ng 8.0 use. I think he sent the disk to eternity.
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Feel free to submit a PR in our official doc, we might have a place for "Best practice" or something like that 🙂