The log file size checker plugin uses an internal class LogSizeTimerTask that inherits from SafeTimerTask. The LogSizeTimerTask have references to build and listener.
Unfortunantly, the LogSizeTimerTask is only cancelled, never completely cleaned up, resulting in one instance of the LogSizeTimerTask being present in the thread pool execution queue for every build that make use of the plugin.
Due to the reference to the build and the listener, those objects are never garbage collected, resulting in every build that was ever built with this plugin active will be kept in memory.
This becomes even more problematic if the build has references to other large objects preventing them as well from being GCed.

Our jenkins master had +10GB of objects that could not be GCed due to this issue, with hundred of thousands of LogSizeTimerTasks in the thread pool execution queue.