A CPU load increase from ~4% to ~25% was seen after mvoing from JBCS 2.4.23 to 2.4.37 with all of that activity seen in the backgound watchdog thread's proxy_cluster_watchdog_func.  This was seen with at least 158 app server instances on the balancer connected via https.  The CPU increase is seen once httpd is started and the app servers join, without any application requests being issued.

The CPU increase is not seen after adding 'EnableOptions off' on 2.4.37.  Also, testing with mod_cluster 1.3.5 modules in 2.4.37 also no longer shows the CPU increase.