ILM is failing to delete closed indices

Elastic Stack Elasticsearch
1

ILM is failing to delete a few closed indices. We are getting the following issue:

policy [<policyName>] for index [<indexName>] on an error step due to a transient error, moving back to the failed step [wait-for-shard-history-leases] for execution. retry attempt [20077]

Cluster is health:

{
    "cluster_name": "es",
    "status": "green",
    "timed_out": false,
    "number_of_nodes": 9,
    "number_of_data_nodes": 6,
    "active_primary_shards": 1339,
    "active_shards": 2678,
    "relocating_shards": 0,
    "initializing_shards": 0,
    "unassigned_shards": 0,
    "delayed_unassigned_shards": 0,
    "number_of_pending_tasks": 0,
    "number_of_in_flight_fetch": 0,
    "task_max_waiting_in_queue_millis": 0,
    "active_shards_percent_as_number": 100.0
}

ILM policy:

"<policyName>": {
        "version": 1,
        "modified_date": "2023-06-28T17:44:22.693Z",
        "policy": {
            "phases": {
                "delete": {
                    "min_age": "122d",
                    "actions": {
                        "delete": {
                            "delete_searchable_snapshot": true
                        }
                    }
                }
            }
        },
        "in_use_by": {
            "indices": [
                <indicesToBeDeleted>
            ],
            "data_streams": [],
            "composable_templates": []
        }
    }

I couldn't find any explanation of what "wait-for-shard-history-leases" means in practice. According to other topics in this forum, ES is able to delete closed indices.

Can someone help?

Thank you.

2

Why the indices are closed?