unable to connect jenkins master to agent machine - jenkins

Question

Jenkins's master can not connect to the slave anymore. It used to work but failed after some time.
I have fixed TCP port for inbound agents. Also, the slave runs with window service. I used to just click slave-agent.JNLP file from the agent machine to start the slave. The window service starts and run but the master can't connect to the slave. I tried to run agent.jar from the command line with/without window service running but keeps getting timeout.
I ran this from the agent machine and got the following error and the master can’t connect to the slave.
java -jar agent.jar -jnlpUrl http:// [MasterServerName]/:8080/computer/Staging%20Node%2001/jenkins-agent.jnlp -workDir "C:\jenkinsagent" -jnlpCredentials [UserName]:[Password]
Dec 06, 2022 10:45:08 AM hudson.remoting.jnlp.Main createEngine
INFO: Setting up agent: Staging Node 01
Dec 06, 2022 10:45:08 AM hudson.remoting.jnlp.Main$CuiListener <init>
INFO: Jenkins agent is running in headless mode.
Dec 06, 2022 10:45:08 AM hudson.remoting.Engine startEngine
INFO: Using Remoting version: 3.29
Dec 06, 2022 10:45:08 AM org.jenkinsci.remoting.engine.WorkDirManager initializeWorkDir
INFO: Using C:\jenkinsagent\remoting as a remoting work directory
Dec 06, 2022 10:45:09 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Locating server among [http://[MasterServerName]/:8080/]
Dec 06, 2022 10:45:30 AM hudson.remoting.jnlp.Main$CuiListener error
SEVERE: Failed to connect to http://[MasterServerName]/:8080/tcpSlaveAgentListener/: Connection timed out: connect
java.io.IOException: Failed to connect to http://[MasterServerName]/:8080/tcpSlaveAgentListener/: Connection timed out: connect
at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:197)
at hudson.remoting.Engine.innerRun(Engine.java:523)
at hudson.remoting.Engine.run(Engine.java:474)
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:242)
at sun.net.www.http.HttpClient.New(HttpClient.java:339)
at sun.net.www.http.HttpClient.New(HttpClient.java:357)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1220)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1156)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1050)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:984)
at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:194)
... 2 more