milo: Bad_SessionIdInvalid "The session id is not valid." - opc-ua

Question

I am getting a "The session id is not valid." exception when reading the value of a node ,but just sometimes,I konw the session is not timeout,so why?
the exception ：
java.util.concurrent.ExecutionException: UaServiceFaultException: status=Bad_SessionIdInvalid, message=The session id is not valid.
at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:395)
at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1999)
at com.ggnykj.smartems.cloud.server.autocontrol.client.OpcClientServer.readNode(OpcClientServer.java:230)
at com.ggnykj.smartems.cloud.server.autocontrol.controller.OpcClientServerController.readNode(OpcClientServerController.java:115)
at com.ggnykj.smartems.cloud.server.autocontrol.server.SaveExOpcData.run(SaveExOpcData.java:59)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: UaServiceFaultException: status=Bad_SessionIdInvalid, message=The session id is not valid.
at org.eclipse.milo.opcua.stack.client.UaTcpStackClient.lambda$receiveResponse$16(UaTcpStackClient.java:367)
at org.eclipse.milo.opcua.stack.core.util.ExecutionQueue$PollAndExecute.run(ExecutionQueue.java:107)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java)
... 3 more
Exception in thread "pool-2-thread-2" java.lang.NullPointerException
at com.ggnykj.smartems.cloud.server.autocontrol.controller.OpcClientServerController.readNode(OpcClientServerController.java:116)
at com.ggnykj.smartems.cloud.server.autocontrol.server.SaveExOpcData.run(SaveExOpcData.java:59)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
my code：
MyX509IdentityProvider x509IdentityProvider = new MyX509IdentityProvider(clientOption.opcServer.getCertFilePath(),
clientOption.opcServer.getPrivateKeyPath());
X509Certificate cert = x509IdentityProvider.getCertificate();
KeyPair keyPair = new KeyPair(cert.getPublicKey(), x509IdentityProvider.getPrivateKey());
OpcUaClientConfig config = OpcUaClientConfig.builder()
.setApplicationName(LocalizedText.english(clientOption.opcServer.getOpcServerName()))
//.setApplicationUri("urn:eclipse:milo:examples:client")
.setApplicationUri("")
//.setCertificate(loader.getClientCertificate())
//.setKeyPair(loader.getClientKeyPair())
.setCertificate(cert)
.setKeyPair(keyPair)
.setEndpoint(endpoint)
.setIdentityProvider(clientOption.getIdentityProvider())
.setChannelLifetime(uint(600000000))
.setSessionTimeout(uint(600000000))
//.setRequestTimeout(uint(5000))
.build();
return new OpcUaClient(config);
private OpcUaClient getOpcClient(OpcServer opcServer){
OpcUaClient client = null;
if(null!=opcClientMap.get(opcServer.getOpcServerId())){
client = opcClientMap.get(opcServer.getOpcServerId());
}else{
try {
ClientOption clientOption = new ClientOption(opcServer);
client = new ClientOptionRunner(clientOption).createClient();
}catch (Throwable t){
logger.error("Error getting client: {}", t.getMessage(), t);
}
opcClientMap.put(opcServer.getOpcServerId(),client);
}
return client;
}
public DataValue readNode(OpcServer opcServer,NodeId nodeId){
OpcUaClient client = getOpcClient(opcServer);
DataValue value = null;
try {
client.connect().get();
value = client.readValue(0.0, TimestampsToReturn.Both, nodeId).get();
}catch (Exception e){
e.printStackTrace();
}
return value;
}