When using the NoActivityTimeOutStrategy the plugin spawns new instances of hudson.plugins.build_timeout.BuildTimeoutWrapper$EnvironmentImpl$TimeoutTimerTask and cancles the previous TimerTask.
However cancelled TimerTasks are not removed from the Timer until they get to the time that they should execute and so for a long running build (days) generating lots of IO with large breaks - and a long inactivity time-out (1 day) you will end up with millions of these TimeoutTimerTask