The "Troubleshooting WMI Windows Agents" page may help as you investigate the issue further.

You may also want to consider using Windows inbound agents rather than using the wmi-agents plugin to manage those agents. Documentation of my experience with those agents in various scenarios is available in a blog post.

You might also want to consider using OpenSSH for Windows to use Jenkins ssh build agents instead of inbound agents. Instructions are included in the ssh build agents configuration guide.

i checked all, but no working 

I installed the Jenkins agent manually and I copied the agent.rar from another working Jenkins agent, but here are the messages in the agent log files

• jenkins-agent.err.log :

Exception in thread "main" java.net.SocketTimeoutException: Accept timed outException in thread "main" java.net.SocketTimeoutException: Accept timed out at java.net.DualStackPlainSocketImpl.waitForNewConnection(Native Method) at java.net.DualStackPlainSocketImpl.socketAccept(Unknown Source) at java.net.AbstractPlainSocketImpl.accept(Unknown Source) at java.net.PlainSocketImpl.accept(Unknown Source) at java.net.ServerSocket.implAccept(Unknown Source) at java.net.ServerSocket.accept(Unknown Source) at hudson.remoting.Launcher.runAsTcpServer(Launcher.java:641) at hudson.remoting.Launcher.run(Launcher.java:396) at hudson.remoting.Launcher.main(Launcher.java:298)

     * jenkins-agent.wrapper.log :

020-09-14 10:31:20,161 DEBUG - Starting WinSW in the service mode
2020-09-14 10:31:20,177 INFO - Starting C:\Program Files\Java\jre1.8.0_261\bin\javaw.exe -Xrs -jar "D:\Tools\Jenkins\agent.jar" -tcp "D:\Tools\Jenkins\port.txt"
2020-09-14 10:31:20,177 INFO - Extension loaded: killOnStartup
2020-09-14 10:31:20,177 DEBUG - Checking the potentially runaway process with PID=3164
2020-09-14 10:31:20,177 DEBUG - No runaway process with PID=3164. The process has been already stopped.
2020-09-14 10:31:20,192 INFO - Started process 10276
2020-09-14 10:31:20,192 DEBUG - Forwarding logs of the process System.Diagnostics.Process (javaw) to winsw.SizeBasedRollingLogAppender
2020-09-14 10:31:20,192 INFO - Recording PID of the started process:10276. PID file destination is D:\Tools\Jenkins\jenkins_agent.pid
2020-09-14 10:31:50,476 DEBUG - Starting WinSW in the service mode
2020-09-14 10:31:50,492 INFO - Starting C:\Program Files\Java\jre1.8.0_261\bin\javaw.exe -Xrs -jar "D:\Tools\Jenkins\agent.jar" -tcp "D:\Tools\Jenkins\port.txt"
2020-09-14 10:31:50,492 INFO - Extension loaded: killOnStartup
2020-09-14 10:31:50,492 DEBUG - Checking the potentially runaway process with PID=10276
2020-09-14 10:31:50,492 DEBUG - No runaway process with PID=10276. The process has been already stopped.
2020-09-14 10:31:50,507 INFO - Started process 10752
2020-09-14 10:31:50,507 DEBUG - Forwarding logs of the process System.Diagnostics.Process (javaw) to winsw.SizeBasedRollingLogAppender
2020-09-14 10:31:50,507 INFO - Recording PID of the started process:10752. PID file destination is D:\Tools\Jenkins\jenkins_agent.pid
2020-09-14 10:32:20,789 DEBUG - Starting WinSW in the service mode
2020-09-14 10:32:20,804 INFO - Starting C:\Program Files\Java\jre1.8.0_261\bin\javaw.exe -Xrs -jar "D:\Tools\Jenkins\agent.jar" -tcp "D:\Tools\Jenkins\port.txt"
2020-09-14 10:32:20,804 INFO - Extension loaded: killOnStartup
2020-09-14 10:32:20,804 DEBUG - Checking the potentially runaway process with PID=10752
2020-09-14 10:32:20,804 DEBUG - No runaway process with PID=10752. The process has been already stopped.
2020-09-14 10:32:20,820 INFO - Started process 10964
2020-09-14 10:32:20,820 DEBUG - Forwarding logs of the process System.Diagnostics.Process (javaw) to winsw.SizeBasedRollingLogAppender
2020-09-14 10:32:20,820 INFO - Recording PID of the started process:10964. PID file destination is D:\Tools\Jenkins\jenkins_agent.pid
2020-09-14 10:32:51,101 DEBUG - Starting WinSW in the service mode
2020-09-14 10:32:51,117 INFO - Starting C:\Program Files\Java\jre1.8.0_261\bin\javaw.exe -Xrs -jar "D:\Tools\Jenkins\agent.jar" -tcp "D:\Tools\Jenkins\port.txt"
2020-09-14 10:32:51,117 INFO - Extension loaded: killOnStartup
2020-09-14 10:32:51,117 DEBUG - Checking the potentially runaway process with PID=10964
2020-09-14 10:32:51,117 DEBUG - No runaway process with PID=10964. The process has been already stopped.
2020-09-14 10:32:51,132 INFO - Started process 10292
2020-09-14 10:32:51,132 DEBUG - Forwarding logs of the process System.Diagnostics.Process (javaw) to winsw.SizeBasedRollingLogAppender
2020-09-14 10:32:51,132 INFO - Recording PID of the started process:10292. PID file destination is D:\Tools\Jenkins\jenkins_agent.pid

You might compare the steps you are taking with the steps described in the Jenkins 2.249.1 upgrade testing blog post.

• Jenkins controller installed from 32 bit MSI, agent with Java Web Start 8u144
• Jenkins controller installed from 64 bit MSI, agent with IcedTea-Web
• Jenkins controller installed from jenkins.war file, agent with IcedTea-Web

bump, Seeing the same response. 
This method of launching slaves is critical as we require this method for a stable test complete integration.
I've gone back through the process of configuring as documented in 

I have had to upgrade my nodes from Windows10 1903 to 2004 to avoid the...
"[2020-09-16 16:33:29] [windows-agents] Installing the Jenkins agent service
[2020-09-16 16:33:29] [windows-agents] Copying jenkins-agent.exe
ERROR: Unexpected error in launching an agent. This is probably a bug in Jenkins
Also: java.lang.Throwable: launched here
at hudson.slaves.SlaveComputer._connect(SlaveComputer.java:283)
at hudson.model.Computer.connect(Computer.java:435)
at hudson.slaves.SlaveComputer.doLaunchSlaveAgent(SlaveComputer.java:787)
at java.base/java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:710)"
Error.

Upon completing this I have attempted to reapply the steps documented under to ensure windows update changes were did not overwrite previously configured settings. https://github.com/jenkinsci/windows-slaves-plugin/blob/master/docs/troubleshooting.adoc 

which previous resulted in a 6 working windows nodes of this control method.

Please can you advise on information that can help you diagnose this problem. This upgrade of jenkins master to LTS has broken out entire UI Testing Capability.

georgelinsdell2 I'm not able to diagnose the problem. I don't use the WMI agents plugin.

I was trying to offer suggestions that would help you and other users with your own investigation into the issue. I use Windows inbound agents that are launched from a command prompt and I use Windows agents that connect to the Windows OpenSSH server provided by Microsoft.