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I keep running into a frustrating situation. Here's what's going on.

Step 1 - I leave my 2019 16" MacBook Pro plugged into an LG 5K Ultrafine monitor. After a while, the screen and the laptop go to sleep. The laptop lid is always closed.

Step 2 - When I wake up the computer, the LG 5K screen never shows anything (it's black). I know the MacBook Pro is awake because I hear interface sounds and I also feel my Apple Watch tap me when it automatically unlocks my machine. No matter what I do with the external keyboard and trackpad, the screen never comes on.

Here's what I've tried:

  • I unplug the computer from the monitor and plug it back in. This makes the screen come back on about 30% of the time.
  • I open the lid of my laptop, wait a while, and the monitor comes on about 70% of the time.
  • I reboot the machine and leave it plugged into the monitor. This works 90% of the time.

Sometimes I get a kernel panic when trying all this and the machine hastily shuts off and I have to boot it up from scratch.

While MacBook Pros have almost always had sleep/wake issues since I first got one in 2007, it's noticeably worse with the 16" MBP. I know this because I also have a 15" MBP for work and it doesn't have these problems with the same monitor on my desk. It wakes the screen right up when I wake up the laptop with the bluetooth keyboard.

Has anyone run into this? Any suggestions?

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On March 26, 2020, Apple released macOS Catalina 10.15.4 which said the following in the release notes:

Fixes an issue with screen brightness for the LG UltraFine 5K display after waking from sleep

I noticed this and upgraded immediately, and so far, it seems to have fixed the issue for me!

I've been able to plug my laptop in and have the LG 5K screen come up right away without the usual shenanigans I normally have to do to get the screen to work.

Hooray!

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  • This upgrade fixed it from me too after suffering for three months through it. – gae123 Mar 28 at 19:51
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The issue has to do with the clock sync. Basically, the Mac "knows" that the monitor is connected (I've verified that EDID data was being received), but since the Mac and the display "won't get on the same page" so to speak, the monitor shows blank.

I'd bet if you were to test this with a Bootcamp install of Windows on the same machine, you'd have no issues. The Windows drivers are just more forgiving than the macOS kexts.

Many times you can solve the issue through hardware by using an active adapter if you are converting the signal (i.e. DisplayPort → HDMI). However, if you're going DisplayPort to DisplayPort, there's nothing the active adapter is going to do to fix it.

You may also want to try powering cycling the monitor (if the power button doesn't work, try unplugging from the mains) while the Mac is awake. This solved it for a number of folks.

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I had the exact same issue (16" MacBook Pro + 5K LG Monitor). I download LG Screen Manager app from the Mac App Store, which updated the monitor's firmware and seems to have solved the issue for me.

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  • Thanks for that tip. I checked that and was already on the latest monitor firmware. – Clifton Labrum Mar 27 at 17:23

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