OPC connection fail from OPC Tag browser to designer

Hi,

We are using Kepware to connect to OPC UA server and exactly after 1 hour of establishing the connection we are facing the following error :

o.o.ua.transport.tcp.io.TcpConnection /*..*.:49320 Error
org.opcfoundation.ua.common.ServiceResultException: Bad_RequestTypeInvalid (code=0x80530000, description=“The security token request type is not valid.”)
at org.opcfoundation.ua.transport.tcp.io.TcpConnection$ReadThread.run(TcpConnection.java:782)

and after every 30 mins of retrying it is throwing the below error :

2018-12-05 10:23:44,995 ERROR [Blocking-Work-Executor-40] o.o.ua.transport.tcp.io.SecureChannelTcp -560875045 Failed to renew security token.
org.opcfoundation.ua.common.ServiceResultException: Bad_ServerNotConnected (code=0x800D0000, description=“The operation could not complete because the client is not connected to the server.”)
at org.opcfoundation.ua.transport.tcp.io.TcpConnection.sendRequest(TcpConnection.java:1083)
at org.opcfoundation.ua.transport.tcp.io.SecureChannelTcp.createSecureChannel(SecureChannelTcp.java:673)
at org.opcfoundation.ua.transport.tcp.io.SecureChannelTcp.access$500(SecureChannelTcp.java:97)
at org.opcfoundation.ua.transport.tcp.io.SecureChannelTcp$8.run(SecureChannelTcp.java:1214)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

Can anyone check what would be possible cause of the issue ?