com.gargoylesoftware.htmlunit.html.ScriptElementSupport#onAllChildrenAddedToPage:

... new PostponedAction(element.getPage(), "Execution of script " + element)...

is very inefficient, because element (e.g. a HtmlScript) is rendered unnecessarily. This eats up all our CPUs, because it renders the whole HtmlScript in toString() in our case. I suggest to use e.g. "Execution of " + element.getClass().getSimpleName() instead or another more reduced string representation.