Update:
For me, a more simple procedure works:
When the DP Screen does not wake up:
1. Standby Computer ( cmd alt eject )
2. Disconnect HDMI Screen
3. Wake up Computer again
4. Reconnect HDMI Screen
Has worked a few times without problems.
For my 2012 mac mini the solution with the adapter cable didn't work (see above )
Thank you! This worked.
For me on Mojave on my i7 Mac Mini (Late 2012) with a Mini Display Port to Display Port cable into my Samsung 34" monitor S34J55x at 3440p 21:9 50hz, this workaround saved me from having to reset my computer when it didn't wake properly.
I did the following:
When the DP Screen does not wake up:
1. Standby Computer (cmd + alt + eject)
2. Turned off my Samsung Screen (long press on the power button)
3. Wake up Computer again (in my case by hard clicking the external trackpad)
4. Turned back on the HDMI Screen (pressed the power button)
And the screen powered up with the login screen
By the way, when it happened again a bit later, I saw the same positive result by simply carrying out the following even quicker procedure:
When the DP Screen does not wake up:
1. Standby Computer (cmd + alt + eject)
2. Wake up Computer again (in my case by hard clicking the external trackpad)
Again the screen powered up with the login screen
Some side notes:
1. This is an intermittent issue for me - I had though it only happened after my computer had not been used for a while since sleeping it (i.e. 24hrs+) but then I saw it a minute or so after sending it to sleep from the menu. The issue didn't happen the next time I slept it from the menu and woke it up shortly after - that time it woke up perfectly hence me saying it's intermittent.
2. When my Samsung S34J55x Monitor doesn't wake up properly from sleep - as others have said - trying to wake it up with the keyboard will make the monitor react - it will light up dimly but with no signal and the in-monitor menu will show the DP input logo but no signal is shown, no matter how many times I click the trackpad or strike the keys!
3. As a newbie to this I've learnt there are various states of sleep on Macs - for example normal
Sleep;
Deep Sleep;
Display Sleep - so it's important to be clear which sleep state their computer is in when the issue occurs. As mentioned earlier on the thread, some of these settings can be adjusted in
Energy Saver Preferences. On my Mac I have the
Display Sleep set to come on after 15 minutes of inactivity, and I have the
Computer Sleep set to 3 hours. It may be that this issue isn't seen under
Display Sleep so for me only happens after 3 hours of inactivity or when I put it to sleep manually using the menu. If that's the case and
Display Sleep doesn't have this issue, then as has been mentioned, it's possible to set the
Computer Sleep setting to Never - which although not ideal for power saving could mean that the Mac will always wake up as it will always only ever be in the
Display Sleep state.
4. The 'Lock the Screen' option on the menu may be the same as
Display Sleep. I have a hot corner set up on the lower left hand corner of the screen which is set to
Display Sleep so that's a nice easy way to
Display Sleep it quickly as you walk away from the computer.
5. Weirdly on my Mac, when it's sent to normal sleep from the menu, sometimes the light on the front of my Mac mini goes off completely and sometimes it pulses in and out. I've seen various pages on the internet including an Apple support article explaining what light combinations (i.e. always on, always off, pulsing etc.) relate to which state, i.e. powered on, powered off, sleep, deep sleep, display sleep, etc. but my Mac doesn't seem to correlate to what it says so I'd be aware if you're trying to work out what state it's in from the Light indicator alone!
6. I use SwitchResX to support my monitor at 3440px x 1440px, have 16GB Ram and I'm on the latest Mojave.
Not sure if any of that is helpful, but just to say thanks again to everyone who's contributed here as this workaround has already and will continue to save me a lot of pain in the future!
