10.12.4 display sleep bug

So. . .

Apple care asked me to reset this that and the other, then wipe and reinstall OS. Problem persists

Repair #1 memory problems blamed. Returned to original Apple RAM. Passed testing. Problem persists

Apple Care advise resetting everything & reinstalling OS. Problem persists.

Repair #2 Replaced Logic Board & PSU. Passed testing.Problem persists

Now Apple Care advising me to reinstall OS.

I've had enough. Apple have had about £1800 off me for this iMac alone (about £6K across all my Apple devices).

Time to insist on on a replacement machine, I think. Very not happy!

I don't think a replacement will help you. This is pure and simple, it's a software bug! I have programmed enough systems in my day to know what is usually a hardware bug and what is software. This is a software bug!!!

Man, I miss Steve. Maybe if he was still around we would not even have this issue in the first place!

Something interesting I found during some experimentation. I have a lock screen which is password protected and when the iMac comes out of sleep mode is when the issue happens with monitors. I found that clicking the magic mouse to wake the system and entering the password immediately upon seeing the iMac screen come to life regardless of whether I can see the password field or not seems to work 90% of the time. It will usually flash the main screen once then all monitors come on equally. I have noticed also that this seems to prevent the second blackout which is usually the deadly one that causes the issues that only a reboot will fix. This may be an issue with the lock screen coming out of sleep mode. I'm going to try disabling the lock screen to see if it makes a difference. Just a wild thought and some experimentation to pass along!

No, Apple will no longer return my emails after several worthless attempts to fix the issue with my machine. I am seriously upset with Apple over this and it will definitely affect my future Mac purchases.

Apple obviously does not care about this issue and I believe there is NO attempt or initiative to fix the problem.

Read this Apple Knowledge Base article.

If your Mac doesn't sleep or wake when expected - Apple Support

The High Sierra upgrade made the problem happen way way less for me, but it has happened a couple of times where one of the side 4k monitors connected to my 5k iMac does not come up after sleep of the monitors. To fix it, I put the screens to sleep and wake them back up after about 1-2 seconds and all the monitors come back up just fine. I have not had to reboot to solve the issue as I had to before, and I have not seen my primary 5k display stay off after sleeping the monitors.

Some odd changes of coming out of sleep are that the side monitors sometimes show a messy splash of yellow mixed with some other colors all over the screens for a second or two before the monitors reset and come on normally. Never happened before High Sierra. Another thing is that it takes longer to come out of monitor sleep and I often type my password and hit return before the screens have reset completely and my password gets cut off and is not accepted. I have to be more patient when bringing my monitors out of sleep and logging in.

Same here with iMac 5K + Dell 4K monitor

Same exact issue here as well, 5k iMac with 2 LG 4k displays hooked up. Started after 10.12.4 update.

I am also experiencing this same issue with similar setup (iMac 5K + LG 34in external monitor). This issue began once the 10.12.4 update was applied.

I have the same issue with the iMac screen black after sleep with an external Asus 4k display

I also tried NVRAM then SMC reset. Didn't help.

I spoke with someone at Apple as well and have since sent him some diagnostic data. Good to know that Apple reads these discussions and that they're being proactive about fixing this issue.

On my case, the shutting the other monitors off and then letting the iMac go sleep works so far. At least this has a 2/2 success rate so far.