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?
Best Answer
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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///// EDIT solved the issue through an external thunderbolt dock
I am using the Thunderbolt 3 Dock of Glyph now. My external screen is connected to its Display Port port. After waking up the screens behave normally. When I take a break, I power off the external screen and power it on before waking up the computer. In the tips I got from Glyph, they do ask you to turn off Energy Saving options when connected to the dock, but it all seem to work fine,