Hello Badger,
Unfortunately there is nothing much in logs which can provide more information about this error.
[2020-01-14T07:57:41,130][INFO ][logstash.outputs.elasticsearch] Using mapping template from {:path=>nil}
[2020-01-14T07:57:41,146][INFO ][logstash.outputs.elasticsearch] Attempting to install template {:manage_template=>{"template"=>"logstash-*", "version"=>60001, "settings"=>{"index.refresh_interval"=>"5s", "number_of_shards"=>1}, "mappings"=>{"_doc"=>{"dynamic_templates"=>[{"message_field"=>{"path_match"=>"message", "match_mapping_type"=>"string", "mapping"=>{"type"=>"text", "norms"=>false}}}, {"string_fields"=>{"match"=>"*", "match_mapping_type"=>"string", "mapping"=>{"type"=>"text", "norms"=>false, "fields"=>{"keyword"=>{"type"=>"keyword", "ignore_above"=>256}}}}}], "properties"=>{"@timestamp"=>{"type"=>"date"}, "@version"=>{"type"=>"keyword"}, "geoip"=>{"dynamic"=>true, "properties"=>{"ip"=>{"type"=>"ip"}, "location"=>{"type"=>"geo_point"}, "latitude"=>{"type"=>"half_float"}, "longitude"=>{"type"=>"half_float"}}}}}}}}
[2020-01-14T07:57:41,159][WARN ][logstash.pipeline ] CAUTION: Recommended inflight events max exceeded! Logstash will run with up to 22000 events in memory in your current configuration. If your message sizes are large this may cause instability with the default heap size. Please consider setting a non-standard heap size, changing the batch size (currently 250), or changing the number of pipeline workers (currently 88) {:pipeline_id=>"tau-cloudepo", :thread=>"#<Thread:0x78aac5c4 run>"}
[2020-01-14T07:57:41,190][INFO ][logstash.outputs.elasticsearch] Installing elasticsearch template to _template/logstash
[2020-01-14T07:57:41,243][ERROR][logstash.outputs.elasticsearch] Failed to install template. {:message=>"Got response code '400' contacting Elasticsearch at URL 'http://elasticsearch_url:9200/_template/logstash'", :class=>"LogStash::Outputs::ElasticSearch::HttpClient::Pool::BadResponseCodeError", :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client/manticore_adapter.rb:80:in `perform_request'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client/pool.rb:291:in `perform_request_to_url'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client/pool.rb:278:in `block in perform_request'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client/pool.rb:373:in `with_connection'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client/pool.rb:277:in `perform_request'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client/pool.rb:285:in `block in Pool'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client.rb:348:in `template_put'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/http_client.rb:86:in `template_install'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/template_manager.rb:21:in `install'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/template_manager.rb:9:in `install_template'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/common.rb:118:in `install_template'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.2.0-java/lib/logstash/outputs/elasticsearch/common.rb:49:in `block in install_template_after_successful_connection'"]}
[2020-01-14T07:57:41,333][INFO ][logstash.pipeline ] Pipeline started successfully {:pipeline_id=>"tau-cloudepo", :thread=>"#<Thread:0x78aac5c4 run>"}
[2020-01-14T07:57:41,407][INFO ][logstash.agent ] Pipelines running {:count=>1, :running_pipelines=>[:"tau-cloudepo"], :non_running_pipelines=>[]}
However there are few logs I got from this pipeline which seems suspicious to me.