使用output.elasticsearch6时出现超时问题

配置如下:
outputs:
- Elasticsearch6:
index: "jlog2es-%{+YYYY.MM.dd}"
cluster: "ELK_FA_SHDI"
hosts: ["172.16.5.8:9300"]
sinff: false
bulkActions: 200
user: elastic
password: iwgroup
启动后一会儿就会发现写入速度不断降低，日志如下(全都是ES链接超时，我确定ES没问题):
2018-12-12 10:58:30.010 [elasticsearch[_client_][transport_client_boss][T#45]] WARN org.elasticsearch.transport.TransportService [TransportService.java:825] - Received response for a request that has timed out, sent [5847ms] ago, timed out [847ms] ago, action [cluster:monitor/state], node [{server0630_nvme_xfs}{v8QeNAcqTC2Pkw2xWFE-WQ}{u-b9Q5nTShumVzFsmTrWyg}{172.16.6.30}{172.16.6.30:9300}{ml.machine_memory=270743080960, ml.max_open_jobs=20, xpack.installed=true, ml.enabled=true}], id [369]
2018-12-12 10:58:30.010 [elasticsearch[_client_][transport_client_boss][T#19]] WARN org.elasticsearch.transport.TransportService [TransportService.java:825] - Received response for a request that has timed out, sent [5847ms] ago, timed out [847ms] ago, action [cluster:monitor/state], node [{server0630_nvme2}{iZ_2w7f8TGS_7hE0MP8jrQ}{rMuOMJx8QcGW6XB_7ME81w}{172.16.6.30}{172.16.6.30:9301}{ml.machine_memory=270743080960, ml.max_open_jobs=20, xpack.installed=true, ml.enabled=true}], id [484]