I'm still getting some major system freezes since about os 10.11.3 or .4.
2012 iMac. First thing that happens, an app freezes. I usually try force quutting it, which appears to close the window, but in activity monitor (which is dreadfully slow) it stays. the computer is otherwise useable, but apps start freezing, including finder, and they cannot be reopened...and the menubar prevents any action. Usually need to resort to hard shutdown with the power button.
a bunch of processes are frozen too, namely escrow security, and often some kind of notification process like distnoted (once I killed this one and everything went again).
I thought it was from waking my mac, but i turned off the sleep and it still happens. I notice that Time machine will often stop working for an age at a time when it happens - since it's supposed to back up every hour, when I come to my computer and it freezes, I can see the history of time machine not working for some time...maybe it's related to that, or maybe some process hangs causing Time Machine to stop backing up.I dunno.
but it's like once a week (was more often when I had sleep on).