Wow... thanks for posting this link! I've been fighting this very problem (random GUI freeze-up's, requiring a forced reboot) for about a month, and had no clue as to what caused it or what could be done to work around it. Based on this link (to Jamf Nation) the problem was introduced when OS X Security Update 2016-003 was applied to El Capitan 10.11.6. The bad news is we'll have to wait on Apple to acknowledge the problem and provide a fix.