[_doc, doc] _Type Issue

[dbt4u]

Since a couple of weeks we have some Elastic-Instances on which we did not get any statsd-Messages into ElasticSearch. All this Messages end with:

{"type":"illegal_argument_exception","reason":"Rejecting mapping update to [statsd-6.3.3-2020.11.23] as the final mapping would have more than 1 type: [_doc, doc]"}

We have made no changes on purpose since around 1 Year or so.

Any Ideas? Even how we can try to find the cause or a work-a-round?

ELS: 7.4.2
Statsdbeat: 6.3.3
OS: Amazon Linux

[dbt4u]

Ok, now we have deleted the index pattern and all indizes inside ELS. We did not see the "_doc vs. doc" Message inside statsdbeat-logs anymore. But the ELS-Logs bothers us now with:

elastic-search-master | "stacktrace": ["org.elasticsearch.index.mapper.MapperParsingException: Failed to parse mapping [_doc]: Root mapping definition has unsupported parameters: [doc : {_meta={version=6.3.3}, dynamic_templates=[{fields={path_match=fields., mapping={type=keyword}, match_mapping_type=string}}, {docker.container.labels={path_match=docker.container.labels., mapping={type=keyword}, match_mapping_type=string}}, {statsd.ctx={path_match=statsd.ctx., mapping={type=keyword}, match_mapping_type=}}, {strings_as_keyword={mapping={ignore_above=1024, (...)

[dbt4u]

Ok

Beat > ELS:
6.8.5 > 7.4.2: sends "_type > doc". This works on the half of our Machines.
7.1.2 > 7.4.2: sends "_type > _doc". Seems a bit more future-proof until 8.x where _type is gone finally.