10.12.4 display sleep bug

I have been turning off my second monitor before the iMac display goes to sleep and that seems to avoid the display bug. However I forgot to turn off the second monitor earlier today so I got the black screen of death. I was able through a few power cycles of the Dell monitor to get the lock screen login to show up on it. Once I logged in, it became the only display so I got the desktop and dock back. When I looked at the display setting under system settings it only shows the Dell monitor. When I look at the system information (from About This Mac) under Graphics/Display it only show the DELL P2715Q as the only display. So for some reason, the built-in iMac display is not recognized by the running system. Since I don't know of a way to kick the monitor from the command prompt, I will probably have to reboot the system to gain back the iMac monitor.

I will try shutting off my two LG monitors in the morning before I leave to see if that helps when I come back home after work. I can tell everyone else this about what I have;

- MacBook Pro, Late 2013 - fully updated, connected to a Dell 24" Monitor (1080p) with no issues.

- MacBook Pro, Early 2015 - fully updated, has been connected to 1 of the 2 LG 4K monitors without issues.

- iMac 27" (Late 2013) - fully updated, has been connected to an Apple Cinema Display (24") and Dell 24" without issues... ever.

- MacBook Air (Mid 2013) - fully updated, has no issues connected to pretty much any monitor I try.

I know I have too many computers, I also have Mac Mini's and they are hooked up to some Dell 4K's but since none of them are new, they only run at 1080p but do so without issues.

So it seems that this issue for my case is isolated to the iMac 27" 5K and Thunderbolt Displays or Thunderbolt Hubs + Displays...

I also received a phone call from Apple regarding this issue, and I have sent them the sysdiagnose file and requested info. I am very impressed with their attention to this problem, they are certainly working toward a resolution. I'll post again if I hear any news.

Same issue with iMac i7 with 5K display and 10.12.4 with 2 external 2560x1440 monitors attached via Thunderbolt to DisplayPort cables - Acer B326HUL and Acer K272HUL. No HDMI adapters involved with the iMac.

Since the Acer monitors are shared with other systems (the monitors have multiple inputs so the other systems connect to the monitors via HDMI), I do not have the luxury of turning them off when the iMac sleeps so I have had to disable turning off the displays in Energy Saver.

This is a very disappointing regression!

Just spoke to Apple support... They suggested resetting the SMC and (wait for it) reinstalling the entire MacOS (although they didn't ask me to erase and reformat the disk the way a certain competitor would)!

Nope. Not going there. Just bought the machine a few months ago and I'm not going to kill a day doing that. I bought this machine because I was having display problems with the external monitors on my old iMac.

We did the SMC reset and that seems to have fixed it - did a quick test with a 1 minute timeout on the Power Saver and the iMac screen came back. Set it to 15 minutes and I'll find out later today whether that makes any difference.

I think the SMC reset is only a temporary fix. I tried that yesterday and things seemed to be fixed. The computer also woke up this morning just fine. I then did some other work, can back and the computer was back to the internal display not waking (the external Dell monitor does wake).

Clearly something in the 10.12.4 update broke the way Power Saver handles "wake up" when you have 4K or WQHD external monitors plugged in. Resetting SMC every week or so is a pretty lame solution. Do we all have to go back to unplugging our computers to save power when we're not using them since that has the side-effect of resetting SMC.

It's kind of like Apple assumes that if you have a 5K iMac, you don't need to plug in external monitors. Well, we do. A lot of us do. So please fix this.

These are the facts I have so far on this issue. Its possible some of them only apply to my system.

1) Apple is aware of the problem. I have spoken to them and they are working on the issue as others also reported. It seems they are trying to gather system diagnostics of iMacs in their broken states. I have no idea how much progress they've made but I do know they're still trying to gather as much as info as they can on the issue. I was able to provide them with such a diagnostics file while my iMac screen would not turn on.

2) The problem is intermittent. I have seen it fail in just 30 seconds. I’ve also seen it not fail for over a day with several successful wake ups.

3) When the iMac screen fails to wake up, sometimes the external monitor comes on, sometimes it doesn’t. I have had instances where the iMac screen does not wake up but the external monitor does. But I’ve also had instances where neither turned on but I know the system was actually awake.

2) Resetting NVRAM/SMC doesn’t help. Though it may be a very short term fix. Hard to tell due to the intermittent nature of the issue.

3) Turning off external monitor before going to sleep is a workaround. Then turn it back on after wake up. Of course, unplugging external monitor is also a workaround.

4) The issue definitely started right after updating to macOS 10.12.4.

5) I did attempt a fresh install on my iMac and then went straight to 10.12.4 without installing any other software or even logging into iCloud. The issue still occurred.

Have the same issue with iMac 5k + 2 other displays setup. The main iMac 5k quite often does not wake up from the sleep mode, but other 2 displays do. The left one acts as a primary and nothing helps (manual sleep and then wake up again, switching off the screen etc.), just reboot. Really annoying.

So far for me shutting off the two external monitors before the iMac goes to sleep is still working for me and while it is a work around it at least works.

I have re-installed the OS, reset everything several times with little success. But as long as shutting of the external monitors work for now I am ok with it till the Apple Engineers can figure it out. I don't like it but cannot fix it by complaining or otherwise.

I have this same issue.

Details: Macbook Air, early 2014, external Acer S241HL monitor via Thunderbolt. Reset SMC and NVRAM to no effect.

I actually had this issue, though far less frequently, before I upgrated to 10.12.4. Now, however, it happens every time the Air sleeps.

I too have been in touch with Apple regarding this. I've supplied them with the sysdiagnose and a file called "iMac.spx". The AppleCare rep (Todd Seydel) has really been very responsive so I'm hoping this can be resolved soon. For the moment I've just turned off power save on my displays and set it to a black screen saver. Not really any sort of power saving but at least I don't have all three monitors lit up 24/7. As Bryston said, I too will post if I hear anything. But hopefully we'll see an OS update soon.

I have the same problem with an original Apple Cinema Display (DVI connected).

It become appears after some time. Not only the sleep does not work, but "blank screen" hot corner does not work anymore too—login screen appears instantly. Really annoying, turning off MacBook Pro every time I need to go away from computer is not fun.

same issue with a late 2016 MacBook Pro 15" and a Dell 42" 4K monitor. Extremely annoying as one has to force shutdown the machine and reboot it. I'm not amused apple to get a new bug built in in a 10.x.4 Release!
When is this going to be fixed?