I have observed this behavior on irc.gimp.net as well.

I think we have a similar issue, internally reported as: https://www.drupal.org/node/2159903

When I restart jenkins I get this RuntimeException:

IRC notifier plugin: Sending notification to: #aegir
IRC notifier plugin: There was an error sending notification to: #aegir
java.lang.RuntimeException: Waiting for mode response interrupted
at org.pircbotx.Channel.getMode(Channel.java:133)
at hudson.plugins.ircbot.v2.IRCConnection.send(IRCConnection.java:276)
at hudson.plugins.ircbot.v2.IRCConnection.send(IRCConnection.java:268)
at hudson.plugins.im.IMPublisher.sendNotification(IMPublisher.java:379)
at hudson.plugins.im.IMPublisher.notifyChatsOnBuildEnd(IMPublisher.java:585)
at hudson.plugins.im.IMPublisher.notifyOnBuildEnd(IMPublisher.java:304)
at hudson.plugins.im.IMPublisher.perform(IMPublisher.java:291)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:45)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:804)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:776)
at hudson.model.Build$BuildExecution.post2(Build.java:183)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:725)
at hudson.model.Run.execute(Run.java:1709)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:231)
Caused by: java.lang.InterruptedException
at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:979)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1281)
at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:207)
at org.pircbotx.Channel.getMode(Channel.java:127)
... 15 more

An older RuntimeException from the jenkins log, I guess the first notice of when the connection was lost.

Aug 6, 2014 2:31:18 AM hudson.plugins.ircbot.v2.IRCConnection send
WARNING: Bot is configured to use colors, but channel #aegir disallows colors!
Exception in thread "bot1-input" java.lang.RuntimeException: Waiting for mode response interrupted
at org.pircbotx.Channel.getMode(Channel.java:133)
at org.pircbotx.Channel.getModeArgument(Channel.java:182)
at org.pircbotx.Channel.getChannelKey(Channel.java:239)
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2872)
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2833)
at org.pircbotx.InputThread.run(InputThread.java:115)
Caused by: java.lang.InterruptedException
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1279)
at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:207)
at org.pircbotx.Channel.getMode(Channel.java:127)
... 5 more

Got feedback in another issue: https://issues.jenkins-ci.org/browse/JENKINS-26491

The build-timeout-plugin is not a solution here.

I therefore would like to request some sort of timeout in the instant-messaging plugin.

Herman, are you sure you are talking about the same issue?
Why would you even think that the build-timeout plugin could be a solution to the IRC plugin disconnecting after a long idle time?

Kutzi, I agree that it's not a proper solution. Some form of re-connect would probably be needed.

What I had hoped the build-timeout plugin to solve is to stop a build that is hanging on the notification. A failed build would alert me of an issue, letting me restart Jenkins if needed to get the IRC connection back. The ironic thing is that the notification is an after-build step, that's why the build-timeout plugin did not help.

Without a timeout it could be a week before anyone noticed that the builds have stalled.

Has some similarities with JENKINS-28175

That is: for the error that Herman is reporting.
Alexej's error might be a completely different one. No way to be sure until he clarifies what it means that the bot 'dies'

Herman, on further thoughts your issue seems to be pretty different from the originally reported issue - disconnecting and hanging on notifications is actually a totally different thing.
Isn't it actually what you reported in JENKINS-26491?

@urras: as you changed this to Critical: can you provide more information. I.e. how to reproduce, error entries in log file etc?

@kutzi I will once it happens again on my instance

Exception in thread "bot2-input" java.lang.RuntimeException: Waiting for mode response interrupted
at org.pircbotx.Channel.getMode(Channel.java:133)
at org.pircbotx.Channel.getModeArgument(Channel.java:182)
at org.pircbotx.Channel.getChannelKey(Channel.java:239)
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2872)
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2833)
at org.pircbotx.InputThread.run(InputThread.java:115)
Caused by: java.lang.InterruptedException
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1301)
at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:236)
at org.pircbotx.Channel.getMode(Channel.java:127)
... 5 more

then the entire jenkins instance is stuck as no job can finish, stuck indefinitely in "IRC notifier plugin: Sending notification to:...."

require a hard restart to get the thing moving again.

We just had this exact issue effect us, had to restart to get moving again as well.

Exception in thread "bot4-input" java.lang.RuntimeException: Waiting for mode response interrupted
at org.pircbotx.Channel.getMode(Channel.java:133)
at org.pircbotx.Channel.getModeArgument(Channel.java:182)
at org.pircbotx.Channel.getChannelKey(Channel.java:239)
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2872)
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2833)
at org.pircbotx.InputThread.run(InputThread.java:115)
Caused by: java.lang.InterruptedException
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1301)
at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:236)
at org.pircbotx.Channel.getMode(Channel.java:127)
... 5 more