Unexpected Reboots

Are the restarts due to kernel panics? OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem." - Apple Sump

If so post a recent panic log Mac OS X: How to log a kernel panic - Apple Support

I have exactly the same computer (mine is 1.2TB fusion drive) , exactly the same symptoms after the 10.11.4 update with no earlier problems, exactly the same experience at the local Apple Store.

Subsequent Apple telephone call yesterday with Apple Customer Service prompted the reply from the assistant, after consulting a senior advisor, that this is somehow "normal" i.e. the clean system restore carried out by the Apple Store over their network has somehow become corrupted and I should use Command R and do yet another system restore. She agreed to phone back today to see if I have had any further problems.

I did what they said, and then last night had the usual -128 'unclean shutdown' diagnostic. Now awaiting phone call.

Meanwhile I thought I would try the last option I have: i.e. restoring my last 10.11.3 Time Machine backup and going from there.

Previously, before contacting Apple I had tried to do this and an error came up telling me it could not erase the iMac hard disk, and I ended up in an endless restore circle unable to get back to a normal reboot and disk utility found no HD, so obviously the HD had been semi-deleted!!

This time that did not happen, the HD was deleted and I am currently in an 8 hour wait (3.1% so far) while the old system is restored.

I'll let you know later where I get to today. If 10.11.3 works fine for more than a day or so, then it is clearly a 10.11.4 problem.

PS: This iMac was new at beginning of December and had to have a new screen by middle of January. Hence my quality assurance doubts about these new iMacs, originally thinking my hard disk was failing. I'm more convinced now that this is a 10.11.4 issue and my 30 year loyalty to Apple is not too much in doubt.

Apple call-back: new assistant informed of the latest developments and concludes with me that it may be an issue with 10.11.4 after all and restoring 10.11.3 will be decisive.

IF I get problems with 10.11.3, then we both conclude it has to be hardware. Only then can I consider future options - if it is hardware, then QA is then definitely a serious consideration. At this price for an iMac, I couldn't afford to rely on them further for my crucial freelance medical work.

At my age plan B is always imperative, so if I had not still got my old iMac (5 years old, never a problem and still going strong) I would be in a financial/professional black hole!

Fingers crossed 10.11.3 works and the only question then will be waiting for a fully compatible OSX 10+ to arrive ...

I have the same machine and same problem. There is another thread on this issue that I responded to here 5k iMac reboots on it's own after installing 10.11.4

Bottom line is that it seems to be affecting a number of different users with late 2015 Retina iMacs and the spontaneous rebooting problem began with the installation of 10.11.4 whereas no such problem occurred with 10.11.3 and earlier.

Hi, just checking in to report that I also have the same system, same problem. My 2015 5K Retina iMac has been randomly rebooting with "Previous shutdown cause: -128", about once a day, since installing 10.11.4. I've reset the SMC and re-installed fresh from an erased disk using recovery install, but the behavior persists.

Restoring 10.11.3 yesterday from Time Machine backup after 8 hours went OK and I was hopeful of a cure.

Unfortunately, at 23:20 I got the usual black screen of death and reboot, this time without needing to log in again.

Then today at 12:46 the screen went dead again but this time rebooted into Log-in mode.

Conclusion: the 10.11.4 update has nothing to do with things, even if it might have triggered the fault in some people's cases.

Comparing responses here with the stories on the other 5k iMac reboots on it's own after installing 10.11.4 thread, there are several slightly differing scenarios, but the root problem is the same: a limited edition expensive iMac with serious QA problems, whether in hardware or software. In my case, I already had a hardware problem with a new screen required after only 45 days from new. Now this!

Where we go from here, I don't know, but I shall be back to a long conversation with Apple right now to push things on - using up time I really don't have to spare.

Anybody know if there is any chance of a decent refund?

I could get 6 reliable Lenovo PCs for this money and continue earning my income in peace with 5 backup machines ...

I had a long conversation with a Senior Support Advisor and can call him back directly from now on.

They agreed to collect my computer and use an Approved Repair Service provider.

I discussed a lot of the issues others like yourselves have brought to light, and the opinion seems to be that it is hardware more than software, especially when I said I had restored 10.11.3 and still have the same problem - in fact 10.11.3 has just crashed out back to log-in THREE times in the last half hour.

Further to your comment above, I have a wireless magic trackpad 2 but a wired keyboard on my machine - the very odd thing is that not only does the keyboard freeze with the screen before the black reboot screen appears, but also the bluetooth connected trackpad - normally this has a physical movement and audible click, and only by moving the lock switch is this turned off. So the freeze must also turn off the physical mechanism via the bluetooth connection.

Certainly the Senior advisor and the service provider both asked me today about any connected peripherals. You may have a point, but I still think it is a more complex hardware issue and we are clutching at straws. See the other thread for the range of self-fixes already tried without success.

One commentator raised the idea of an AMD graphics fault which showed similar symptoms in a games machine he previously had with an AMD inside. Since I had a screen fault that was cured by fitting a new screen one month after buying this iMac, I have to wonder if the graphics connection might be an underlying cause, hence the odd times when the computer crashes but comes straight back to life from the black screen without requiring a log in - it is as if the screen had just given up with an overload of some kind and rebooted itself without affecting the main OS itself. Anybody any ideas??

Best of luck.

Apple Repair guy phoned to say there was a logic board and power supply fault, replaced and now doing final testing.

Should have iMac back tomorrow.

Ive got the same problem, bought iMac in Feb, ever since update it started the random rebooting and developed a problem with the bluetooth. When it is first switched on the bluetooth is disabled, the only way to solve it is to restart the iMac via keyboard shortcut. (i use a wired keyboard).

Trouble is I'm over the 14day return period so could you please advise me on who to contact in regards to getting this solved , its draining me.

Thanks in advance.

Kind Regards