I found following logs in the upgraded master node:
[o.e.x.m.e.l.LocalExporter] [master-1] monitoring index template [.monitoring-logstash] does not exist, so service cannot start (waiting on master)
[o.e.x.m.e.l.LocalExporter] [master-1] waiting for elected master node [{master-3}{djCtwvYuSgWcgQ2DnbvitQ}{sdvoobvCS6ig6brEOUmMPA}{<ip>}{<ip>:9300}{xpack.installed=true}] to setup local exporter [default_local] (does it have x-pack installed?)
[o.e.x.m.e.Exporters ] [master-1] skipping exporter [default_local] as it is not ready yet
The last one keeps repeating every 10 seconds.
X-pack monitoring is enabled on all the nodes.
I saw below issues and it seems like I'm facing problems due to different versions of elasticsearch.
skipping exporter [default_local] as it is not ready yet
Rebuilt node, logs say waiting for local exporter
Rolling upgrade sequence of node types
Will the issue be resolved if I upgrade all the nodes to 6.8.3?