The retrofit-image action fails when passed a focal image ID

The octavia-diskimage-retrofit action 'retrofit-image' fails when passed a focal image ID.
This deployment uses glance simple streams sync to add images to glance (see attached bundle).

ubuntu@litleo-cpe-7efe6852-56b2-4284-a908-74da2c7a946b:~/project$ openstack image list
+--------------------------------------+---------------------------------------------------------------+--------+
| ID | Name | Status |
+--------------------------------------+---------------------------------------------------------------+--------+
| 316578f4-a4dc-4163-81de-6038ba4823df | auto-sync/ubuntu-bionic-18.04-amd64-server-20200407-disk1.img | active |
| 50ef49a7-a812-410f-a668-ceb4e604f033 | auto-sync/ubuntu-focal-20.04-amd64-server-20200428-disk1.img | active |
| b3b8c5a1-4267-4281-8f1d-7e408cdec039 | auto-sync/ubuntu-trusty-14.04-amd64-server-20191107-disk1.img | active |
| 9d163be7-fe5d-485b-991f-d6b85afdaf00 | auto-sync/ubuntu-xenial-16.04-amd64-server-20200430-disk1.img | active |
+--------------------------------------+---------------------------------------------------------------+--------+

ubuntu@litleo-cpe-7efe6852-56b2-4284-a908-74da2c7a946b:~/project$ juju run-action -m foundations-maas:openstack --format=yaml --wait octavia-diskimage-retrofit/leader retrofit-image source-image=50ef49a7-a812-410f-a668-ceb4e604f033
unit-octavia-diskimage-retrofit-0:
  UnitId: octavia-diskimage-retrofit/0
  id: "21"
  message: Command '['octavia-diskimage-retrofit', '-u', 'stein', '/var/snap/octavia-diskimage-retrofit/common/tmp/tmpuesy46kk',
    '/var/snap/octavia-diskimage-retrofit/common/tmp/tmpxpat8a6z']' returned non-zero
    exit status 1.
  results:
    Stderr: |
      All snaps up to date.
    Stdout: |
      lxc
  status: failed
  timing:
    completed: 2020-05-04 21:05:25 +0000 UTC
    enqueued: 2020-05-04 20:59:41 +0000 UTC
    started: 2020-05-04 20:59:45 +0000 UTC

No issues observed when the bionic image ID is given.