I understand that with xpack installed you need to pass credentials along with a request. In this case, I have uninstalled xpack on all nodes in the cluster and restarted the cluster.
On cluster restart, the status is red and inspection of the logs shows the following error message.
[2019-11-12T09:51:51,876][DEBUG][o.e.a.a.c.n.i.TransportNodesInfoAction]  failed to execute on node
Caused by: org.elasticsearch.ElasticsearchSecurityException: missing authentication token for action [cluster:monitor/nodes/info[n]]
at org.elasticsearch.xpack.security.support.Exceptions.authenticationError(Exceptions.java:39) ~[?:?]