The agents went offline and we found the ChannelClosedException in the log. We could not bring the agents online till we restarted the Jenkins master. This happened several times since we upgraded to the 1.565.3 version of Jenkins LTS.

[EnvInject] - Loading node environment variables.
[EnvInject] - [ERROR] - SEVERE ERROR occurs: java.lang.InterruptedException
ERROR: [description-setter] Error while parsing logs for description-setter
hudson.remoting.ChannelClosedException: channel is already closed
at hudson.remoting.Channel.send(Channel.java:540)
at hudson.remoting.Request.call(Request.java:129)
at hudson.remoting.Channel.call(Channel.java:742)
at hudson.EnvVars.getRemote(EnvVars.java:404)
at hudson.model.Computer.getEnvironment(Computer.java:912)
at jenkins.model.CoreEnvironmentContributor.buildEnvironmentFor(CoreEnvironmentContributor.java:29)
at hudson.model.Run.getEnvironment(Run.java:2221)
at hudson.model.AbstractBuild.getEnvironment(AbstractBuild.java:885)
at hudson.plugins.descriptionsetter.DescriptionSetterHelper.setDescription(DescriptionSetterHelper.java:47)
at hudson.plugins.descriptionsetter.DescriptionSetterPublisher.perform(DescriptionSetterPublisher.java:70)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:756)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:720)
at hudson.model.Build$BuildExecution.post2(Build.java:182)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:669)
at hudson.model.Run.execute(Run.java:1731)
at hudson.matrix.MatrixRun.run(MatrixRun.java:146)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:232)
Caused by: java.io.IOException
at hudson.remoting.Channel.close(Channel.java:1030)
at hudson.slaves.ChannelPinger$1.onDead(ChannelPinger.java:110)
at hudson.remoting.PingThread.ping(PingThread.java:120)
at hudson.remoting.PingThread.run(PingThread.java:81)
Caused by: java.util.concurrent.TimeoutException: Ping started on 1426396728206 hasn't completed at 1426396968206
... 2 more
[EnvInject] - [ERROR] - SEVERE ERROR occurs: channel is already closed
Finished: FAILURE