Unknown error - Cluster sharding

Can anyone explain me about the below error
Click this link to know the details Multiple sharding in a Cluster

sharding-akka.actor.default-dispatcher-24 akka://sharding/system/sharding/region1Coordinator/singleton/coordinator - Message [akka.cluster.sharding.ShardCoordinator$Internal$Register] from Actor[akka.tcp://sharding@127.0.0.1:2554/system/sharding/region1#361794112] to Actor[akka://sharding/system/sharding/region1Coordinator/singleton/coordinator] was not delivered. [35] dead letters encountered. If this is not an expected behavior, then [Actor[akka://sharding/system/sharding/region1Coordinator/singleton/coordinator]] may have terminated unexpectedly, This logging can be turned off or adjusted with configuration settings ‘akka.log-dead-letters’ and ‘akka.log-dead-letters-during-shutdown’. 15:05:01.426 INFO sharding-akka.actor.default-dispatcher-2 akka://sharding/system/sharding/region1Coordinator/singleton/coordinator - Message [akka.cluster.sharding.ShardCoordinator$Internal$Register] from Actor[akka.tcp://sharding@127.0.0.1:2553/system/sharding/region1#-1618412502] to Actor[akka://sharding/system/sharding/region1Coordinator/singleton/coordinator] was not delivered. [36] dead letters encountered. If this is not an expected behavior, then [Actor[akka://sharding/system/sharding/region1Coordinator/singleton/coordinator]] may have terminated unexpectedly, This logging can be turned off or adjusted with configuration settings ‘akka.log-dead-letters’ and ‘akka.log-dead-letters-during-shutdown’.

Please advice me on this

Thanks