Failure to create ephemeral VM when no architectures are found on the VM host

hmm it seems your VM Host is missing its architecture. Can you share the output of `maas $PROFILE vm-hosts read`? Additionally, was the VM Host added with "register as a KVM host" on deployment, or was this an existing host that was added to MAAS' VM Hosts?

So I checked again the architecture, and it is defined, but error still occurs. The vm host that I am working on is actually the one that has maas installed. Important info is also, that this error didn't occur when working with older maas version (I think it was 2.8), instead ephemeral machine was created as expected.

We were not able to reproduce this on 3.2 by only requesting it to allocate a machine. We need more details about your setup:

1) what kind of KVM are you running (LXD or Virtsh) and which version?
2) is this a fresh MAAS install or have you been upgrading it since 2.x?
3) the output of `maas $PROFILE vm-hosts read`
4) the output of `maas $PROFILE machines allocate`)

So we figured it out what was the problem - we had 2 hosts, one of them was uninitialized virsh host (cores:0, memory:0):

root@maas:/home/ubuntu# maas admin machines allocate
list index out of range
root@maas:/home/ubuntu# maas admin vm-hosts read
Success.
Machine-readable output follows:
[
    {
        "default_macvlan_mode": "",
        "capabilities": [
            "composable",
            "dynamic_local_storage",
            "over_commit",
            "storage_pools"
        ],
        "host": {
            "system_id": "kwxmgm",
            "__incomplete__": true
        },
        "total": {
            "cores": 4,
            "memory": 8192,
            "local_storage": 22884122624
        },
        "storage_pools": [
            {
                "id": "default",
                "name": "default",
                "type": "zfs",
                "path": "/var/snap/lxd/common/lxd/disks/default.img",
                "total": 22884122624,
                "used": 0,
                "available": 22884122624,
                "default": true
            }
        ],
        "type": "lxd",
        "id": 1,
        "pool": {
            "name": "default",
            "description": "Default pool",
            "id": 0,
            "resource_uri": "/MAAS/api/2.0/resourcepool/0/"
        },
        "architectures": [
            "amd64/generic"
        ],
        "zone": {
            "name": "default",
            "description": "",
            "id": 1,
            "resource_uri": "/MAAS/api/2.0/zones/default/"
        },
        "memory_over_commit_ratio": 1.0,
        "available": {
            "cores": 4,
            "memory": 8192,
            "local_storage": 22884122624
        },
        "name": "crisp-skunk",
        "cpu_over_commit_ratio": 1.0,
        "used": {
            "cores": 0,
            "memory": 0,
            "local_storage": 0
        },
        "version": "5.6",
        "tags": [
            "pod-console-logging",
            "virtual"
        ],
        "resource_uri": "/MAAS/api/2.0/vm-hosts/1/"
    },
    {
        "default_macvlan_mode": null,
        "capabilities": [],
        "host": {
            "system_id": null,
            "__incomplete__": true
        },
        "total": {
            "cores": 0,
            "memory": 0,
            "local_storage": 0
        },
        "storage_pools": [],
        "type": "virsh",
        "id": 50,
        "pool": {
            "name": "default",
            "description": "Default pool",
            "id": 0,
            "resource_uri": "/MAAS/api/2.0/resourcepool/0/"
        },
        "architectures": [],
        "zone": {
            "name": "default",
            "description": "",
            "id": 1,
            "resource_uri": "/MAAS/api/2.0/zones/default/"
        },
        "memory_over_commit_ratio": 1.0,
        "available": {
            "cores": 0,
            "memory": 0,
            "local_storage": 0
        },
        "name": "sadsa",
        "cpu_over_commit_ratio": 1.0,
        "used": {
            "cores": 0,
            "memory": 0,
            "local_storage": 0
        },
        "version": "",
        "tags": [
            "pod-console-logging"
 ...