Other thing I was thinking (and trying without success), was to maintain open the htmlunit WebClient, and not to do a client.closeAllWindows(); only when servlet destroy. I was trying to cache and make the page request faster, but... maybe we have to try again.
By the way, as we are using cloudflare CDN, I've added this rule:
kune.cc/*escaped_fragment*
Cache level: Aggressive caching
Generation of static html pages for crawler using htmlunit is provoking a lack of performance sometimes. We want to avoid this controlling how and when htmlunit processes are executed.