I found following log in debug.log for the read_replicas of a causal cluster. when this issue came those read replica servers are not showing in the cluster list when we did the :sysinfo.
after restart the process on that server then the error is gone and able to discover the read_replica in the cluster list. We are using 3.5.4 version
2021-07-27 17:43:41.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
2021-07-27 17:43:41.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
2021-07-27 17:43:46.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
2021-07-27 17:43:51.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
2021-07-27 17:43:56.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
2021-07-27 17:44:01.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
2021-07-27 17:44:01.131+0000 WARN [o.n.c.d.HazelcastClient] Uncaught exception
java.lang.NullPointerException
