Requests to delete * or _all index templates should exclude any templates for hidden data streams. Because of the restriction on deleting templates for data streams and the fact that there are now a number of automatically-created hidden data streams such as ILM history, a high percentage of requests to delete all templates will likely fail. In order to delete the template for a hidden data stream, the data stream itself must first be deleted and then the index template may be deleted either individually or with a wildcard that is more selective than *.

We consider this a tactical solution to the immediate problem. Longer term, a more intuitive and holistic approach to resolving entities in Elasticsearch, perhaps something along the lines of the expand_wildcards option, would be preferred.