any idea on this issue ..
00:21:33.245 [Native-Transport-Requests-1] ERROR org.apache.cassandra.transport.Message - Unexpected exception during request; channel = [id: 0x9417fcb0, L:/
127.0.0.1:9143 - R:/
127.0.0.1:52260]
java.lang.AssertionError: null
at org.apache.cassandra.locator.TokenMetadata.firstTokenIndex(TokenMetadata.java:1065) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.locator.TokenMetadata.firstToken(TokenMetadata.java:1079) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.locator.AbstractReplicationStrategy.getNaturalEndpoints(AbstractReplicationStrategy.java:107) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.service.StorageService.getNaturalEndpoints(StorageService.java:3834) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.service.StorageProxy.performWrite(StorageProxy.java:1074) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.service.StorageProxy.mutate(StorageProxy.java:621) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.service.StorageProxy.mutateWithTriggers(StorageProxy.java:851) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.cql3.statements.ModificationStatement.executeWithoutCondition(ModificationStatement.java:439) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.cql3.statements.ModificationStatement.execute(ModificationStatement.java:425) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.cql3.QueryProcessor.processStatement(QueryProcessor.java:225) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.cql3.QueryProcessor.process(QueryProcessor.java:256) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.cql3.QueryProcessor.process(QueryProcessor.java:241) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.transport.messages.QueryMessage.execute(QueryMessage.java:116) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.transport.Message$Dispatcher.processRequest(Message.java:686) ~[cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.transport.Message$Dispatcher.lambda$channelRead0$0(Message.java:592) ~[cassandra-all-3.11.6.jar:3.11.6]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) [?:?]
at org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$FutureTask.run(AbstractLocalAwareExecutorService.java:165) [cassandra-all-3.11.6.jar:3.11.6]
at org.apache.cassandra.concurrent.SEPWorker.run(SEPWorker.java:113) [cassandra-all-3.11.6.jar:3.11.6]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-common-4.1.59.Final.jar:4.1.59.Final]
at java.lang.Thread.run(Thread.java:834) [?:?]
00:21:33.366 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 1000 milliseconds
00:21:34.388 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 2000 milliseconds
00:21:36.400 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 4000 milliseconds
00:21:40.405 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 8000 milliseconds
00:21:48.406 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 16000 milliseconds
00:22:04.421 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 32000 milliseconds
00:22:36.438 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 64000 milliseconds
00:23:40.453 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 128000 milliseconds
00:25:48.459 [cluster1-reconnection-0] ERROR com.datastax.driver.core.ControlConnection - [Control connection] Cannot connect to any host, scheduling retry in 256000 milliseconds