[v 7.17] Component Template Alias not working

[parosio]

Hello,
I needed to update a legacy template to add an alias, but the operation fails (legacy template are deprecated).

I created a set of components to replicate the existing template

then included them in a new index template:

The Request is:

PUT _index_template/tptt_eni_tp_test_new
{
  "index_patterns": [
    "eni-test-tp*"
  ],
  "composed_of": [
    "cptt_eni_test_settings",
    "cptt_eni_tp_mapping",
    "cptt_eni_tp_aliases"
  ]
}

but the preview does not contain the aliases from the alias component:

{
  "template": {
    "settings": {
      "index": {
        "number_of_shards": "2",
        "number_of_replicas": "0"
      }
    },
    "mappings": {
      "dynamic_templates": [],
      "properties": {
        "@timestamp": {
          "type": "date"
        },
        "Attack_Type": {
          "type": "text",
          "fields": {
            "keyword": {
              "type": "keyword"
            }
          }
        },
[  ... cut ...  ]
        "subsidiary": {
          "type": "text",
          "fields": {
            "keyword": {
              "type": "keyword"
            }
          }
        },
        "uploadTime": {
          "type": "date",
          "format": "yyyy/MM/dd HH:mm:ss.SSS"
        }
      }
    },
    "aliases": {}
  }
}

The alias component seems fine:

GET _component_template/cptt_eni_tp_aliases

{
  "component_templates" : [
    {
      "name" : "cptt_eni_tp_aliases",
      "component_template" : {
        "template" : {
          "aliases" : {
            "eni-tp-subs-angola" : {
              "filter" : {
                "term" : {
                  "subsidiary.keyword" : "angola"
                }
              }
            },
[  ... cut ...  ]
            "eni-tp-subs-kenya" : {
              "filter" : {
                "term" : {
                  "subsidiary.keyword" : "kenya"
                }
 } } } } } }
  ]
}

When a document is posted to a new index like eni-test-tp.test-component the settings and mappings are correct, but it has none of the expected aliases.

The only solution I found is to add the alias section during the index_template creation itself, as the composition seems rejecting the alias component.

Am I doing something wrong?

Regards,
Paolo