Elasticsearch version 7.11.1

Snapshot and restore: If an index is deleted while the cluster is concurrently taking more than one snapshot then there is a risk that one of the snapshots may never complete and also that some shard data may be lost from the repository, causing future restore operations to fail. To mitigate this problem, set snapshot.max_concurrent_operations: 1 to prevent concurrent snapshot operations:

PUT _cluster/settings
{
  "persistent" : {
    "snapshot.max_concurrent_operations" : 1
  }
}

This issue is fixed in Elasticsearch versions 7.13.1 and later. It is not possible to repair a repository once it is affected by this issue, so you must restore the repository from a backup, or clear the repository by executing DELETE _snapshot/<repository name>/*, or move to a fresh repository. For more details, see #73456.