5k iMac reboots on it's own after installing 10.11.4

During the weekend random reboots on my iMac returned—with a vengeance. I had 4 or 5 reboots daily. The pattern and symptoms are always the same: the Magic Trackpad 2 and screen instantly freeze, without any warning or error message. At that point, I can’t click the trackpad at all: it is effectively locked. After some 10 seconds the iMac reboots: the screen goes black until the chime sounds. No error messages.

While rebooting, the trackpad unlocks. Having logged in, all open applications and windows reappear and I can resume working.

I’ve tried to localize pertinent entries in Console, without success: there are simply too many entries, and I don’t know what to look for. Last week I ran memtest86, which gave no error messages. I’ve also run TechTool Pro, DiskWarrior, Disk Utility etc., apparently my iMac has a clean bill of health.

Because I've little to lose, yesterday I've updated to 10.11.5: I ran DiskWarrior from a TechTool e-drive, repaired permissions and installed the Combo Update from that drive.

So far, so good, although while typing this message, my Magic Trackpad did in fact suddenly lock, loosing its connection. This happened twice, within five minutes.

No system wide freeze and random reboot, though. The Trackpad just locks for some twenty seconds, during which I can't click. A message says that I've lost the connection, after which it automatically reconnects and a confirming message appears. Weird.

I have a 27 inch Mid-2015 iMac 5K Retina and I just started having this problem yesterday. I have been running 10.11.4 for a while with no problems. Then yesterday I was on the web with Firefox and all of a sudden the cursor froze and the computer went black only to return a few moments later at the login screen.

I don't think the computer totally restarted as I did not hear the Apple sound. The same thing happened again today but after logging in there was a message saying the computer had restarted and there was a diagnostic report that was sent to Apple with details about the crash I suppose.

Thankfully this has only happened twice that I know about. I hope someone can figure out something soon.

I also have a Late 2015 Retina 27' iMac 4.0GHZ with AMD Radeon R9 M395X. After upgrading to 10.11.5, I got a random freeze followed by a reboot. I guess it still hasn't been fixed yet.

No it's not fixed with 10.11.5, I've have 3 reboots in the last 24hours and again nothing in the log.

So far today my iMac has restarted on its own at least three or four times within a two hour span. This is getting ridiculous as I cannot get anything done. Someone at Apple has to be following this thread and needs to figure something out.

Mac 5K retina 27 inch Mid-2015

OS 10.11.4

I tried to do the update for OS 10.11.5 today and it said the update was not verified.

I guess the only option we have at this point is to get Apple support involved. I've scoured the internet looking for a solution and have found none so far. I've read that people have taken the machines back to the Apple store to have it worked on. I'm really hoping this turns out to be a software or firmware issue that Apple can repair. If/When my iMac freezes again, I'll have to call and open a support request and hope for the best.

I called Apple tech support and they got me to do a SMC reset.

http://support.apple.com/kb/HT201295?viewlocale=en_US

They are going to call back tomorrow to see if that worked.

So far, so good: no more random reboots since I updated to 10.11.5, and no more disconnecting and locking of Magic Trackpad 2. I'm knocking on wood, though.

Greg23, Just curios if you've had any reboots since doing the SMC reset?

RIch, sadly later that night it restarted at least 10 times before I just shut it down. Then things got even weirder this morning around 8 AM when my computer started up all by itself. It never finished loading all the way, just got to the Apple logo and the progress bar along with a lot of computer code on the left of the screen.

So I did not wait for my 7 PM call back to see if the SMC reset worked. I called them up immediately and they couldn't figure it out over the phone so I took it in to the local Apple repair shop.

I hope to find out something by Monday. I will post again when I know something.

I just sat through two reboots on a one month old 27 iMac 5K late 2015. Frustrating to say the least. It came with 10.11.4 and had the problem before and after updating to 10.11.5. I have owned an Apple since 1986. This is the first time I am this dissatisfied. Come on Apple. Step up.

Same issues as everyone else: Freezing while using (mail and safarI0 and while not using iMac late 2015. No problems with 10.11.3 until I updated to 10.11.4 and got the freezes/random reboots. Went back to 10.11.3 via Time Machine backup but freezes/restarts continued. Did everything anyone ever suggested about the problem (disabled plug-ins, extensions, Apple Diagnostics, Disk Utility First Aid, turned off Web Gl, turned off automatic backups, and more). Never get any error messages just freeze and restart with chimes. Did EtreCheck but no issues found. So updated to 10.11.5 via combo update...STILL HAVING FREEZES/RESTARTS. Will call Apple today but not hopeful given what everyone else is experiencing. I live 160 miles away from the nearest Apple repair so hope it's not hardware. Thanks for all the information everyone is giving.

My iMac showed the same symptoms like all the other iMacs in this thread. I've tried all troubleshooting steps, including SMC-Reset, clean OS Install, etc. - nothing helped. Like others in this thread already suggested, i called the apple support and sent it to the authorized service provider/repair center. Last week my iMace came back - they changed the logicboard and the powersupply. There were no reboots, since it came back - so i guess it was really a hardware-fault. I hope it won't come back...

Another interesting thing i've noticed, is that it came back with a newer boot-rom version (IM171.0105.B08, before it was IM171.0105.B07).

To those who are still looking for a solution, i just can recommend to send it to apple and let it be repaired. Good luck to all of you 🙂.

A couple of days, and stil going strong: no more random reboots for me. I'm keeping my fingers crossed...

After I read sst42's post, I checked my own Boot-ROM version: it's IM171.0105.B08.

I'm not sure if I had IM171.0105.B07 before updating to 10.11.5. If not so, I had my random reboots with the B08 version.

Alas, after a few quiet days, random reboots have returned. First, the Magic Trackpad 2 locked, but (unlike other events in the past) no random reboot followed. I switched the trackpad off and on, and resumed working. A little while later, I was away for an hour or so. When I returned, my iMac (Retina 5K, 27", Intel Core i5, 3,3 GHz, ROM-version IM171.0105.B08, SMC-versie (systeem): 2.34f2) had rebooted on its own. As far as I can tell, all my iMac's random reboots were preceded by the trackpad suddenly locking so that clicking the trackpad is physically impossible.