I have upgraded ES version from 6.2.3 to 6.8.4 after upgrade all indices and cluster is RED. We have 3 nodes cluster and nodetool status showing nodes status UN.

Datacenter: dc1

Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns Host ID Rack
UN 192.168.. 124.02 GiB 256 ? ********************************** rack1
UN 192.168.. 115.82 GiB 256 ? ********************************** rack1
UN 192.168.. 120.9 GiB 256 ? ********************************** rack1

I am getting below error in logs

2022-04-13 12:10:36,675 WARN [elasticsearch[192.168..][masterService#updateTask][T#1]] MasterService.java:712 executeTasks org.elasticsearch.cluster.service.MasterService$$Lambda$2197/1556570788@46b2def6
java.lang.IllegalArgumentException: can't add node {192.168..}{f9ed38c8-b7e0-4944-a0fe-4af6b5c6eb84}{f9ed38c8-b7e0-4944-a0fe-4af6b5c6eb84}{192.168..}{192.168..:9300}{DISABLED}{dc=dc1, rack=rack1}, found existing node {192.168..}{2c19J9KBSlWuOA_iSwufGw}{2c19J9KBSlWuOA_iSwufGw}{192.168..}{192.168..:9300}{ALIVE}{rack=rack1, dc=dc1} with same address
at org.elasticsearch.cluster.node.DiscoveryNodes$Builder.add(DiscoveryNodes.java:649)
at org.elassandra.discovery.CassandraDiscovery$GossipCluster.nodes(CassandraDiscovery.java:237)
at org.elassandra.discovery.CassandraDiscovery.nodes(CassandraDiscovery.java:943)
at org.elassandra.discovery.CassandraDiscovery$RoutingTableUpdateTaskExecutor.execute(CassandraDiscovery.java:553)
at org.elasticsearch.cluster.service.MasterService.executeTasks(MasterService.java:704)
at org.elasticsearch.cluster.service.MasterService.calculateTaskOutputs(MasterService.java:302)
at org.elasticsearch.cluster.service.MasterService.runTasks(MasterService.java:227)
at org.elasticsearch.cluster.service.MasterService$Batcher.run(MasterService.java:158)
at org.elasticsearch.cluster.service.TaskBatcher.runIfNotProcessed(TaskBatcher.java:150)
at org.elasticsearch.cluster.service.TaskBatcher$BatchedTask.run(TaskBatcher.java:188)
at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:681)
at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:252)
at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.run(PrioritizedEsThreadPoolExecutor.java:215)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

curl http://192.168.*.*:9200/_cluster/health?pretty
{
"cluster_name" : "*",
"status" : "red",
"timed_out" : false,
"number_of_nodes" : 1,
"number_of_data_nodes" : 1,
"active_primary_shards" : 0,
"active_shards" : 0,
"relocating_shards" : 0,
"initializing_shards" : 0,
"unassigned_shards" : 1162,
"delayed_unassigned_shards" : 0,
"number_of_pending_tasks" : 0,
"number_of_in_flight_fetch" : 0,
"task_max_waiting_in_queue_millis" : 0,
"active_shards_percent_as_number" : 0.0
}

java -version
openjdk version "1.8.0_312"
OpenJDK Runtime Environment (build 1.8.0_312-8u312-b07-0ubuntu1~18.04-b07)
OpenJDK 64-Bit Server VM (build 25.312-b07, mixed mode)

Linux ip-192-168-*-*5.4.0-1060-aws #63~18.04.1-Ubuntu SMP Mon Nov 15 14:31:31 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

curl http://192.168.*.*:9200/test_2020_11_04/allocation/explain?pretty=true
{
"error" : {
"root_cause" : [
{
"type" : "remote_transport_exception",
"reason" : "[192.168..][192.168..:9300][indices:data/read/get[s]]"
}
],
"type" : "action_request_validation_exception",
"reason" : "Validation Failed: 1: test.allocation table does not exists;"
},
"status" : 400
}

PS: I haven't copied data from other node manually. I am upgrading existing node.