iMac (Retina 5K, 27-inch, Late 2015) Randomly Restarts Without Errors

I agree with Michael, in the iMac 17,1 models the problem doesn't appear to be as easy as an SMC reset. That, along with:

1) Wiping the hard drive and reinstalling the operating system

2) Restoring to a Time Machine Backup and going back to 10.11.3

3) Leaving it with apple authorized techs (not an Apple Store Genius bar, in a rural area) and paying 50 bucks service charge and losing my work Mac for several days.

4) At the behest of Apple engineers, I took out my CDW 32GB of RAM and replaced it with the 8GB Apple RAM, and performed Capture.App of data from the Mac to try and diagnose the problem.

The restarts have continued in spite of replacing my CDW RAM with with the Apple RAM.

All of this was precipitated by upgrading to 10.11.5.

I am waiting now on a logic board replacement or a genius software fix (like, 10.11.6, perhaps?). I'll complain if Apple somehow doesn't provide the same service to me it has provided to others here.

If I don't hear from the apple senior advisor I've been speaking with (Vince Aker) I'm calling him first thing tomorrow get a status update.

Yes, I too have tried resetting SMC multiple times and it doesn't affect the problem (and, like you bendean, none of those other proposed solutions work.) I just thought that in Michael's case, since the plug thing seems to matter for him (doesn't make a difference for me), it might be a different thing going on. But a) I'm no tech expert, just spitballing and b) I share your (and everyone on this board's) frustration with the fact that this does seem to be an issue baked into a small subset of 17,1s yet there doesn't seem to be much of a recognition of such on Apple's part. Hopefully that will change; everyone is posting encouraging signs that it might do so.

Just adding my same sad story that I am having the exact same problem with random restarts on my iMac17,1, delivered Feb. 3, 2016. Random restarts, multiple times per day. Chatted with Apple Support. Did Apple Hardware test. Results came back with no errors. Don't have time to do the exhaustive procedures outlined by bendean. I use 32 GB 3rd Party Crucial Memory. But looks like it's not a RAM issue.

Not a RAM issue as I have used 3 different sets of RAM in my machine and the random restarts happened with all three sets of RAM. Apple wants me to sit in front of my machine this Friday and go through a bunch of diagnostics. Seems they fail to understand we all got these machines for business and giving up my Friday afternoon is going to cost me time which translates into money. Then I will have to leave it at my Apple store for over a week while they run further tests - with no guarantee they will fix it as others here have discovered.

I simple solution and one that would save all of use frustration is to simply exchange our machines for new ones or refund us all of our money. I smell a class action lawsuit building. Can you say E-Books...

Advice I received from engineering, via my Apple Advisor, was to uninstall the Ghostery Safari extension. Something in logs indicated that Ghostery syncing was causing the random reboots.

So I've done that and we'll see what happens. Note: Random reboots starting probably does roughly coincide with my installation of Ghostery. That a Safari extension could cause the whole system to reboot is, not great.

Interesting. Do let me/us know if that works. I, for one, am skeptical. I don't have/never have had any Ghostery extensions on my computer, nor do I even use Safari. Of course, your problem might have a different cause than mine. But this is advice is similar to what I and others have gotten here: "Oh it's a piece of software!" They've given me very similar advice: "we've looked at logs, it's software X, just delete it." The only thing is: the software that they identified wasn't ALWAYS the cause in the logs, just a cause that popped up in a log or two. (As I think is the case with you, most times w my computer, there are NO logs for the freezes/restarts.) So in my case, at least, these rogue software crashes appear to be more symptom than cause. But like I said: please keep us updated. Maybe this is something that is different from computer to computer, tho I still am extraordinarily skeptical that that's the case.

Agreed Jon––I'm supremely skeptical that this Safari extension is the problem. It's similar to Apple engineers saying "it's the third party RAM!" but on a software front.

FYI, the Apple Senior Advisor did not touch base with me this week, so I'm not pleased about that. I left a voicemail this morning on his line with my case #, and I hope that finally next week we'll see some action. The computer restarted twice just this morning, and averages at least 1 random restart a day.

Jon, when you say there are no logs, do you mean that the Console doesn't show any info on "Previous Shutdown" ? Because mine shows "Previous Shutdown -128" every single time it does this random restart.

Bendean, to clarify: Console DOES show previous shutdown cause (as -128) every time, which I actually didn't realize until just now when I went back through previous logs (I have been keeping a rigorous manual log of freeze/restart times, so compared that to old Console logs).

What I was referring to when I said there are "no logs" is that, like I said, I've been recording crash times down to the second (keep time.is up on my phone, jot down the exact time when crash happens), and then looking back over the Console logs for what's going on at that exact moment. And 95% of the time, in the logs, there is NOTHING happening in the log; a couple minutes before or something, there will be a notice of some process(es) running, then nothing, then, boom, 45-60 seconds after the freeze time, the boot process will start up. The other 5% of the time, there will be some random error message, "x process caused kernel panic", and it's those random messages that have led Apple to focus on individual software things. And again, removing those pieces of software did nothing.

-Jon

The possible unifying factor that could make it the same problem with different causes across computers would be if there is an underlying issue with sandboxing. My Ghostery extension was installed via the Safari Extension gallery, and my understanding is that those extensions are sandboxed in the same way as an app from the Mac App Store. A piece of software like this really shouldn't be able to take down the whole system unless there is a underlying issue. As I remember Jon, you had a whole slew of errors, including kernel panics, that I didn't have.

The reason I've always been skeptical of it being a hardware problem is that it will happen when the system is asleep and not under load at all. Marginal pieces of hardware tend to fail when the system is being pushed not when idle. If everyone showing up in these threads said it happened when they were putting the system under load, then I would really believe it was a faulty piece of hardware.

Anyway, we will see what happens. I haven't had a reboot in several days as it is.

Interesting you mention that Greg. Knock on wood, luckily, my iMac hasn't had a random restart while I am rendering out video (that is, using Adobe Media Encoder to encode 1080p internet video files) which it encodes like butter from 10 minutes-2 hours depending on video complexity and length.

When rendering out video, the computer is usually idle, chugging away at the render.

The iMac does crash when I'm editing video, surfing the web, reading emails, editing photos, playing music in iTunes, etc. There's no rhyme or reason to it.

Keep in mind this is anecdotal, however––I haven't done a long form 4k export that requires the computer to stay on 4-8 hours since before this started, so it is possible the computer could also crash during those renders, which would/will be an absolute nightmare for my business.

For a $4,000+ editing machine, that level of uncertainty is unacceptable.

Just to put the "third party app" to rest:

The retailer did a clean install on my iMac with 10.11.3 to see if there was a problem with anything I had installed, and it still reboots.

I've become real good at saving my work a lot since I "upgraded" to this iMac.

How are things coming along for those that are talking to Apple Care Outreach?

-KJ

It's entirely possible that we're all having the same end result with different causes. In other words, there may have been something introduced in the last few OS updates that causes the system to fail to handle some error states gracefully and instead results in a reboot as a default fallback.

kj, THAT was my experience also. As soon as I updated to 10.11.5, BOOM, even a clean install of 10.11.3 fixed nothing. For a software problem to follow you like that seems really weird to me, but again, I'm no engineer, so I can't speak with authority on that. Either way, the problems is persistent and will not go away, and that's supremely troubling and needs to be addressed seriously by Apple. I hope that is what is happening, but so far communication has been very limited and I've had to push for what I have got.

Not great. The Outreach person explained to me that they weren't actually taking over my case but just making sure it got to the engineers. Haven't heard anything from them in a week and a half. A new Apple Support tech (number 5) said he was going to set me up for in-home service (because I'm 2.5 hours from an Apple Store and an hour from a service center) and a change of my logic board. Got all the way to the end of the process and determined that i couldn't get in-home service after all. So I have to pack everything up, haul it to the service center and watch them do everything that I've already done over the last two and a half months.

This is probably no help at all...but, I had the same issue going on last week for several days...freeze and reboot, no errors. It has simply stopped as I have had no incidents in days. Probably spoke too soon...will return tomorrow! Ha!

Hope not! Watch this space.