External Displays won't come back on

I updated last night and left my 16” MBP connected to my monitor overnight. MBP crashed while I was sleeping. So, no fixes in this update.

I wonder if Apple reads this thread?

Hope someone has reported this problem to an Apple Service Center.

Amazing, 8 pages deep 6 months, and still no fix from Apple, that a quality product right there?

That work-around does not work on my Mac. I often put my mac into sleep, and go to meetings. When i come back, it's crashed. Testing to have the lid open for today..

Another frustrated user - with BenqSW271 directly connected via USB-C cable. Same issues.

For sure! I did not update my OS, so it's still at 10.15.1.. That's a shame..

Is anyone else seeing resolution of this issue with 10.15.6? I can’t test because my laptop is currently in to Apple for the issue.

Lol! I want to believe you but I am so terrified of updating since I haven’t had an issue while working in 10.15.1. How long has it gone without issue?

This worked for me however the resolutions and screen arrangement settings were reset. Not a huge issue but will become frustrating if it persists. MBP 16 is just days old. So far not too happy with it.

I was told a long time ago by an Apple service tech that resetting the PRAM once wasn’t a complete reset. Not sure if this is still the case. I reset mine twice yesterday and so far, problem solved. Not sure it’ll work long term but I do recommend resetting it more than once by holding the keys down until the thing restarts a second or third time.

I have had the same issue, even after updating to 10.15.3.

I seem to have figured out a workaround (other than unplugging my LG UltraFine display. I found that the following works for me:

In Energy Saver settings for the Power Adapter:

1. Check "Prevent computer from sleeping automatically when display off"
2. Uncheck "Put hard disks to sleep when possible"
3. Both "Wake for network access" and "Enable Power Nap" are also checked

For batter power, I just have the put disk to sleep option enabled like normal as I don't use an external display when not connected to power.

I have been running on this for a few days. Although my screen will sleep like normal (I have mine set to sleep after 15 minutes), it appears that the disk sleep being turned off seems to have been the culprit for my external display not coming back on--unless I rebooted and re-plugged in the display after boot up.

I would prefer to have the disk sleep, but until Apple fixes this somehow, I will use these settings. I'm happy now--it works like it used to on my MacBook Pro 13" which didn't have these issues.

Could anybody else try this to confirm it works? 😃

This solved the external display issue. However, I have found that when connected to an external display the MacBook Pro really heats up significantly.

I've also noticed that other processes seem to eventually stop functioning properly. For example, this morning the print monitor would not launch. I was able to print, but the app would hang on launch. I had to restart the computer to get it functioning again. No idea if this is related or a different issue all together.

I have started to disconnect the computer from the monitor whenever I am not actively using it....

So far my solution was the same as raydmark's https://discussions.apple.com/thread/250931552?answerId=252305393022 PLUS that I set "Turn Display off after" to Never. At the end of the work or day, I manually set the machine to sleep.

Without the [ "Turn Display off after" --> Never ] addition, I had occasional problems when MBP goes into the screen saver mode. And it possibly also cause the connected Thunderbolt port going stale, leading to the crazy black-white cycle, and further occasionally also the monitor color map screwups. By then I don't know what is the cause and what the effect. So to be safe, I let the whole rig eat up electricity.

For the past week, that worked.

(I have several USBC devices (mostly HDs) attached to the back of the monitor as well as a test iphone. When one of the problems occur prior to the solution above, I found myself having to unplug the connection btwn MBP16 and the LG monitor in the dark which occasionally solved the issue. But it also led to the HDs improperly disconnected. I suspect that might have done bad things not only the storage but also to the Thunderbolt port (i.e. flickering cycles). When that happened, I had to re-boot with PROM/VROM? refresh to fix.)

I just upgraded today. 10.15.4 on 16" MBP with 5500.

The computer went into kernel panic while plugged in, sleeping and connected to external monitor. Going back to the hacky "Prevent computer from sleeping with display off." Absolutely ridiculous.

Panic(cpu 8 caller 0xffffff8015091b2c): Sleep transition timed out after 180 seconds while entering darkwake on way to sleep. Suspected bundle: com.apple.iokit.IOGraphicsFamily. Thread 0x74.
Backtracing specified thread
Backtrace (CPU 8), Frame : Return Address
0xffffff875ef7b900 : 0xffffff8014a471e8 
0xffffffa785acb9b0 : 0xffffff80149433f1 
0xffffffa785acba20 : 0xffffff8014941c2f 
0xffffffa785acba70 : 0xffffff8014a442e9 
0xffffffa785acbab0 : 0xffffff8014a43b4b 
0xffffffa785acbae0 : 0xffffff7f98599ced 
0xffffffa785acbb10 : 0xffffff7f985b2f75 
0xffffffa785acbb20 : 0xffffff7f9859ccb9 
0xffffffa785acbbb0 : 0xffffff7f985a2549 
0xffffffa785acbc50 : 0xffffff80150020cf 
0xffffffa785acbcc0 : 0xffffff801501a770 
0xffffffa785acbd60 : 0xffffff80150028b9 
0xffffffa785acbdb0 : 0xffffff8015017e1b 
0xffffffa785acbe50 : 0xffffff801501424e 
0xffffffa785acbea0 : 0xffffff8015011d40 
0xffffffa785acbef0 : 0xffffff8015011bd9 
0xffffffa785acbf30 : 0xffffff801502d43e 
0xffffffa785acbf70 : 0xffffff801502ca36 
0xffffffa785acbfa0 : 0xffffff80148c713e 
      Kernel Extensions in backtrace:
         com.apple.iokit.IOGraphicsFamily(575.1)[D47CA481-C5E5-3F03-9B04-6634DF5F3121]@0xffffff7f98591000->0xffffff7f985e1fff
            dependency: com.apple.iokit.IOPCIFamily(2.9)[1B1F3BBB-9212-3CF9-94F8-8FEF0D3ACEC4]@0xffffff7f95311000

It did include it in the bug fixes. I found it in the release notes.

This update also includes bug fixes and other improvements.

• High Dynamic Range output to HDR10-compatible third-party displays and TVs connected with DisplayPort or HDMI
• OAuth authentication support with Outlook.com accounts for improved security
• CalDav migration support when upgrading to iCloud reminders on a secondary device
• Resolves an issue where text copied between apps may appear invisible when Dark Mode is active
• Fixes an issue in Safari where a CAPTCHA tile may display incorrectly
• Resolves an issue where Reminders may send notifications for completed reminders
• Fixes an issue with screen brightness for the LG UltraFine 5K display after waking from sleep