After nearly two weeks of hope that the update to OS X El Capitan 10.11.6 might fix its freezing bug, which was introduced on 21 March 2016 in version 10.11.4, it is clear that some models of Mac still freeze just as they did before. In fact, as far as I can tell from your reports and my experience, 10.11.6 has not fixed a single bug listed here.
My experience yesterday on this iMac17,1 (2015 5K display) was exactly the same as many previous freezes. I had used the Mac fairly lightly during Saturday, but had worked during the evening. There had been no crashes, unexpected quits, or other untoward events before I packed up just before midnight and went to bed. I leave my iMac set to sleep its display, but not to sleep the ‘computer’, as no matter what I set hard disk sleep to do, enabling system sleep shuts the internal hard disk down. Thus the Mac is left with the display asleep (after a delay of an hour), but otherwise running all night.
Yesterday morning, when I came down at about 6:30, it was sat showing the login screen, having automatically restarted at about 03:30 following a sudden freeze which was so catastrophic as to prevent any error messages or warnings from appearing in the logs.
Here are the log entries over the period, with my comments:
31/07/2016 03:17:57.614 CalendarAgent: [com.apple.calendar.store.log.caldav.coredav] [Refusing to parse response to PROPPATCH because of content-type: [text/plain; charset="utf-8"].]
31/07/2016 03:17:57.711 CalendarAgent: [com.apple.calendar.store.log.caldav.coredav] [Refusing to parse response to PROPPATCH because of content-type: [text/plain; charset="utf-8"].]
Those are frequent entries which occur every 20-30 minutes, for no apparent reason.
31/07/2016 03:26:57.000 syslogd: ASL Sender Statistics
This is also a routine entry relating to sending logs to Apple, I believe.
31/07/2016 03:33:01.000 bootlog: BOOT_TIME 1469932381 0
31/07/2016 03:33:03.000 syslogd: Configuration Notice:
ASL Module "com.apple.AccountPolicyHelper" claims selected messages.
Those messages may not appear in standard system log files or in the ASL database.
This is the beginning of the restart sequence, which occurred six minutes after the previous log entry. Normally the autorestart occurs within a minute or two of freezing, so other reports should have been made after 03:30 – of which there are none.
During the restart, the journal had to be replayed
31/07/2016 03:33:03.000 kernel: CoreStorage: fsck_cs has finished for group "7F469F41-150A-48B4-A5D0-61497AADB942" with status 0x00
31/07/2016 03:33:03.000 kernel: thr Composite Disk alg="bloomclock" unit_nbytes=131072
31/07/2016 03:33:03.000 kernel: Got boot device = IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/RP17@1B/IOPP/SSD0@0/AppleSATAExpress/PRT0@0/IOAHCIDevice@0/AppleAHCIDiskDriver/IOAHCIBlockStorageDevice/IOBlockStorageDriver/APPLE SSD SM0128G Media/IOGUIDPartitionScheme/Diagnostics@2/CoreStoragePhysical/Macintosh HD/Macintosh HD
31/07/2016 03:33:03.000 kernel: BSD root: disk2, major 1, minor 8
31/07/2016 03:33:03.000 kernel: jnl: b(1, 8): replay_journal: from: 116482048 to: 117215232 (joffset 0x1d28e000)
31/07/2016 03:33:03.000 kernel: jnl: b(1, 8): examining extra transactions starting @ 117215232 / 0x6fc9000
31/07/2016 03:33:03.000 kernel: jnl: b(1, 8): Extra txn replay stopped @ 117297152 / 0x6fdd000
31/07/2016 03:33:03.000 kernel: jnl: b(1, 8): journal replay done.
31/07/2016 03:33:03.000 kernel: hfs: mounted Macintosh HD on device root_device
Once this replay is complete, the startup volume is mounted correctly, and ready to use.
The quoted cause for the restart was code -128:
31/07/2016 03:33:04.000 kernel: Previous shutdown cause: -128
No error value -128 seems to make any better sense, but more generally -128 is a ‘user cancelled’ error.
Freezes are also reported to continue on iMac 2012 models, but I do not know whether other models which were affected by them in 10.11.4 and 10.11.5 – notably some recent MacBook Pros – are any better with 10.11.6.
No release version of any Unix-like operating system should ever collapse in this way.
That Apple has released not one, not even two, but three successive versions of OS X 10.11 over a four month period which suffer this cataclysmic failure demonstrates its total disinterest in supporting Mac users. As ever, if there were a realistic alternative, I would switch, after more than 27 years as an avid Mac user.