This seems to me like a network issue. When this happens, please login to the agent machine, and run below command to see if it works:
telnet servername 8810

Some error like this, it is not match the test build time tag, it maybe cause by the network
or some cancel failed:

========
2022-02-28 13:34:27,385 [Thread-12] ERROR com.pmease.quickbuild.Quickbuild - Error connecting server.
    com.caucho.hessian.client.HessianRuntimeException: com.caucho.hessian.client.HessianRuntimeException: Error connecting 'http://servername:8810/service/connect'
        at com.caucho.hessian.client.HessianProxy.sendRequest(HessianProxy.java:285)
        at com.caucho.hessian.client.HessianProxy.invoke(HessianProxy.java:171)
        at com.sun.proxy.$Proxy19.connect(Unknown Source)
        at com.pmease.quickbuild.grid.AgentConnectivityTask.run(AgentConnectivityTask.java:62)
        at java.lang.Thread.run(Thread.java:748)
    Caused by: com.caucho.hessian.client.HessianRuntimeException: Error connecting 'http://servername:8810/service/connect'
        at com.caucho.hessian.client.HessianURLConnection.getOutputStream(HessianURLConnection.java:103)
        at com.caucho.hessian.client.HessianProxy.sendRequest(HessianProxy.java:283)
        ... 4 more
    Caused by: java.net.SocketTimeoutException: connect timed out
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        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.SocksSocketImpl.connect(SocksSocketImpl.java:392)
        at java.net.Socket.connect(Socket.java:607)
        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:1223)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
        at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:990)
        at sun.net.www.protocol.http.HttpURLConnection.getOutputStream0(HttpURLConnection.java:1337)
        at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1312)
        at com.caucho.hessian.client.HessianURLConnection.getOutputStream(HessianURLConnection.java:99)
        ... 5 more

=======
2022-03-15 13:02:09,837 [pool-2-thread-1282] WARN com.pmease.quickbuild.grid.NodeServiceImpl - testGridJob is cancelling job '41ce1f76-80e9-4b55-9baf-91f57379facf'...
2022-03-15 13:02:09,838 [pool-2-thread-1282] WARN com.pmease.quickbuild.grid.GridTaskFuture - Job still exists on job node and cancel command is issued (job id: 41ce1f76-80e9-4b55-9baf-91f57379facf, build id: 661422, job node: test-agent-1:8812)...

Can you please show me the error?

I can check with system log to know it run the test, but don't know which test
check with QB agent log just have some error like QB connect error

The load history is not available yet. You may however check the agent log to see if there is any clue.