Nodes in graylog cluster are lost

Nodes in graylog cluster are lost

## Expected Behavior
I have a GL cluster，You can normally see four nodes in nodes from any of the four nodes，However, at present, there are always nodes online or offline

## Current Behavior
There is a special node. Only 3 nodes can be seen on other nodes. On this node, 4 nodes can be seen

## Possible Solution
none

## Steps to Reproduce (for bugs)

1.click system -> nodes
2.
3.
4.

## Context
This problem makes me feel that there are always problems in the cluster

## Your Environment

* Graylog Version: 3.1.4
* Java Version: 1.8
* Elasticsearch Version: 6.8.6
* MongoDB Version: 3.6
* Operating System: Centos7
* Browser version: Chrome