Bootloader.Bad_error No valid Btrfs found

[building39]

I built a new Ubuntu 20.04.2 server box, and get this error when I do vagrantup`:

ERROR warden: Error occurred: ["INTERNAL_ERROR", "xenopsd internal error: VM = 1b34106f-f42c-a6c0-d257-cb58f27a597a; domid = 89; Bootloader.Bad_error No valid Btrfs found on /dev/sm/backend/4f2600f8-a793-38b0-b3ae-57d7cc6394be/9cf7ba6a-a10b-4608-8f51-026665abdb37\nNo valid Btrfs found on /dev/sm/backend/4f2600f8-a793-38b0-b3ae-57d7cc6394be/9cf7ba6a-a10b-4608-8f51-026665abdb37\nSuperblock bytenr is larger than device size\nTraceback (most recent call last):\n  File \"/usr/bin/pygrub\", line 992, in <module>\n    fs = xenfsimage.open(file, part_offs[0], bootfsoptions)\nIOError: [Errno 95] Operation not supported\n"]
 INFO warden: Beginning recovery process...
 INFO warden: Recovery complete.
ERROR warden: Error occurred: ["INTERNAL_ERROR", "xenopsd internal error: VM = 1b34106f-f42c-a6c0-d257-cb58f27a597a; domid = 89; Bootloader.Bad_error No valid Btrfs found on /dev/sm/backend/4f2600f8-a793-38b0-b3ae-57d7cc6394be/9cf7ba6a-a10b-4608-8f51-026665abdb37\nNo valid Btrfs found on /dev/sm/backend/4f2600f8-a793-38b0-b3ae-57d7cc6394be/9cf7ba6a-a10b-4608-8f51-026665abdb37\nSuperblock bytenr is larger than device size\nTraceback (most recent call last):\n  File \"/usr/bin/pygrub\", line 992, in <module>\n    fs = xenfsimage.open(file, part_offs[0], bootfsoptions)\nIOError: [Errno 95] Operation not supported\n"]
 INFO warden: Beginning recovery process...
 INFO warden: Recovery complete.
ERROR warden: Error occurred: ["INTERNAL_ERROR", "xenopsd internal error: VM = 1b34106f-f42c-a6c0-d257-cb58f27a597a; domid = 89; Bootloader.Bad_error No valid Btrfs found on /dev/sm/backend/4f2600f8-a793-38b0-b3ae-57d7cc6394be/9cf7ba6a-a10b-4608-8f51-026665abdb37\nNo valid Btrfs found on /dev/sm/backend/4f2600f8-a793-38b0-b3ae-57d7cc6394be/9cf7ba6a-a10b-4608-8f51-026665abdb37\nSuperblock bytenr is larger than device size\nTraceback (most recent call last):\n  File \"/usr/bin/pygrub\", line 992, in <module>\n    fs = xenfsimage.open(file, part_offs[0], bootfsoptions)\nIOError: [Errno 95] Operation not supported\n"]
 INFO warden: Beginning recovery process...

Vagrantfile looks like this:

# -*- mode: ruby -*-
# vi: set ft=ruby :

API_VERSION = "2"
PRIVATE_KEY = "~/.ssh/id_rsa"
PUBLIC_KEY  = '~/.ssh/id_rsa.pub'
XCP_HOST    = "xencat"
XCP_USER    = "root"
XCP_PSWD    = "mypassword"

servers=[
  {
    :hostname => "dockcat",
    :ip => "192.168.2.67",
    :box => "building39/focal",
    :ram => 2048,
    :cpu => 2
  }
]

Vagrant.configure(API_VERSION) do |config|
  servers.each do |machine|
    config.vm.define machine[:hostname] do |node|
      node.vm.box = machine[:box]
      node.vm.hostname = machine[:hostname]
      node.vm.network "public_network", bridge: "xenbr0", ip: machine[:ip]
      node.vm.provider "xenserver" do |xs|
        xs.xs_host = XCP_HOST
        xs.xs_username = XCP_USER
        xs.xs_password = XCP_PSWD
        xs.name = machine[:hostname]
        xs.pv = true
        xs.memory = 4096
        xs.use_himn = false
      end
    end
  end

end

Vagrant version: 2.2.16

Installing on XCP-NG 8.1

If I use xs.pv = false the box installs and boots fine.
Should I really be using xs.pv = true?

[psafont]

I'm not sure what's the problem exactly. Unfortunately the vagrant plugin has not been maintained for some years. :(