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I have a MacBook Pro (Retina, 13-inch, Early 2015, macOS High Sierra 10.13.6) which fails to detect an external display after is has woken up from sleep. (Update: Now running macOS Mojave 10.14.5 on a 13-inch 2018 model, and this is still a very annoying issue).

Here's my situation: I have an external monitor hooked up to to the MacBook's display port, I walk away from my computer for a few minutes and it goes to sleep. I come back, and no matter what I try, the only way for the MacBook to detect the external display again is to restart the computer!

I'm using a Mini DisplayPort to DisplayPort cable. I use the MacBook at home as well as at work; I've tried different ports on my computer, different cables, and different monitors; the issue is with the MacBook itself.

It used to be that when this happens, I manually put the MacBook to sleep and wake it up again, and voila, it would detect the external display again. But now the only way to consistently fix the issue is to restart the MacBook.

I've also tried opening the display settings, holding down the alt key, and clicking "Detect Displays". This does nothing.

Any ideas on how to remedy this problem?

  • Exactly same symptoms (MBP 2017). Only reboot helps. Tried to replace all cables, and tried 2 different thunderbolt docking stations. SMC and PRAM resets did not help either. – Dmitry Oct 26 '18 at 17:48
  • forums.macrumors.com/threads/… – Dmitry Oct 26 '18 at 17:59
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    You'd think a trillion dollar company would put up some money to iron this bug that's been around for so long. – Moshe Gottlieb Apr 10 '19 at 4:51
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    Still an issue on the newer macs :'( – cornflakes24 May 18 '19 at 14:30
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    Since there's apparently no solution to this except rebooting or plugging cables around, I suggest that everyone that has this problem creates a bug report at Apple, otherwise they might not notice. I have submitted a bug report including a video of the 2 displays flickering today. – narrowtux Jan 22 at 14:00
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I still have the same issue on a macbook pro 15' 2018.

Unplugging and plugging again the screens helps without having to restart the whole thing... except that all open windows jump to the main screen.

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I've found the system knows the other monitor is there, it just can't rouse it. Fastest work-around I've devised so far:

  1. Open System Preferences
  2. Go to 'Displays'
  3. Click 'Gather Windows'
  4. On the panel for the external display, choose one of the rotation options. (Seems that forces the system to give itself a kick and the external display will wake up, albeit upside down.)
  5. Helpfully, there's a 'Revert' button already focussed. Just press Enter on your keyboard and it'll spin back around.

Done.

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  • That doesn't work for me since it doesn't know the other displays are there, so not "Gather Windows" option. – Gabrie Aug 7 at 13:27
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I experience similar problem and Google brought me here. Though as long as I don't unplug the cable it would always work fine. If I unplug it to take away the laptop and come back again one of my two monitors (the one converted from Thunderbolt to HDMI) won't work. However the other one with Thunderbolt to DisplayPort always works.

My solution is to connect it to a different port and most of time it would just work again.

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