Elasticsearch output connection pool error, with Linux VIP, but still indexing

[javadevmtl (None)]

Hi running 6.2.4

I have the following config...

elasticsearch {
  hosts => ["data6dev.marathon.l4lb.thisdcos.directory:9200"]
  user => "elastic"
  password => "xxxxxx"
  index => "dcos-%{+YYYY.MM.dd}"
}

data6dev.marathon.l4lb.thisdcos.directory:9200 is a Linux VIP which load balances to 3 data nodes.

Logs are being indexed to Elasticsearch, but I keep seeing this error...

[2018-07-10T20:35:54,492][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://elastic:xxxxxx@data6dev.marathon.l4lb.thisdcos.directory:9200/, :path=>"/"}
[2018-07-10T20:35:54,502][WARN ][logstash.outputs.elasticsearch] UNEXPECTED POOL ERROR {:e=>#<LogStash::Outputs::Elasticsearch::HttpClient::Pool::NoConnectionAvailableError: No Available connections>}
[2018-07-10T20:35:54,502][ERROR][logstash.outputs.elasticsearch] Attempted to send a bulk request to elasticsearch, but no there are no living connections in the connection pool. Perhaps Elasticsearch is unreachable or down? {:error_message=>"No Available connections", :class=>"LogStash::Outputs::Elasticsearch::HttpClient::Pool::NoConnectionAvailableError", :will_retry_in_seconds=>4}
[2018-07-10T20:35:54,506][WARN ][logstash.outputs.elasticsearch] Restored connection to ES instance {:url=>"http://elastic:xxxxxx@data6dev.marathon.l4lb.thisdcos.directory:9200/"}