I’m now coming to the end of week fifteen of my struggle to keep macOS 10.11.4 then 10.11.5 running on my iMac without it sporadically freezing. I have run out of ideas as to what to try next, apart from switching to a different Mac.

Since I updated to 10.11.5, this iMac17,1 has continued to freeze unpredictably, at a rate of once every 1-5 days. I cannot recall it keeping going for as long as a week, since I updated to 10.11.4 back in March 2016, although prior to that it had been as rock solid as my previous iMac.

Freezes can occur at any time. Recently, when I stopped it from sleeping, it most commonly froze during the small hours of the morning, between 0130 and 0600, and when I got up I would find it sat at the login screen, waiting for me like a faithful dog. Since then I have let it sleep, so now it more commonly freezes when in use. It has not, so far, frozen when being woken.

Its logs are of no use in identifying the cause. Sometimes there are no log entries for several minutes before the freeze occurs, and the only record seen is of the automatic restart afterwards. At least it has automatically restarted on each occasion, and has never needed my intervention. Whatever is causing this freezing seems sudden, and so catastrophic to the kernel that it stops the Mac dead in the water, without it even writing a farewell in the logs.

When it restarts in front of my eyes now, I hold the Command and R keys to enter Recovery mode, and run First Aid in Disk Utility just to be safe. So far no repairs have been necessary. Every week or two I restart it into hardware test/diagnostic mode (with a wired keyboard and mouse) and check the hardware out. Each time it has reported the tests complete normally. I have also run TechTool Pro and ATOMIC (a specialised memory test tool), and DriveDx, and there are no hardware faults detected.

I have sanitised /System/Library and /Library by hand, and my latest ploy was to uninstall OS X Server, which appears to cause problems for some. Neither has made the slightest bit of difference. Usually when I have performed any cleaning operation such as those it seems to precipitate an earlier freeze, within, say, twelve hours, as if to remind me of my inability to fix the problem.

As uninstalling OS X Server did not help, I have today installed the 10.11.5 Combo updater, but feel sure that that will not make the blindest bit of difference either.

My working conclusion is that these random freezes are the result of a kernel or other low-down component, and were introduced in the 10.11.4 update. Apparently macOS 10.11.6 is now in advanced beta-testing; let’s hope that contains the fix.

If you have your own experience to share here, please do so. I need all the help that I can get.