External Displays won't come back on

It seems that the AMD drivers on the new Macbook Pro 16-inch are a mess, as you can see here: https://discussions.apple.com/thread/250878229 connecting the machine to an external monitor is causing a lot of issues. 10.15.3 didn't fix the fan issue.

I am having similar problems with the 2019 16" i9 and a LG 21.5" 4k Thunderbolt Display. I thought, as well, that 10.5.2 fixed it but it has resumed again.

The issue occurs in two ways:

1. On wake from sleep, both screens flicker in turn, quickly, and neither one takes. The Touch Bar flickers as well. Disconnecting the screen is the only solution.
2. On wake from sleep, the laptop has forgotten the external display and only activates the internal screen. However, USB devices connected to the external display continue to function.

I have tried disconnecting devices from the external display, plugging and replugging, etc. The only thing that works is to restart the MacBook Pro. I had been using this very same setup with a 2016 MacBook Pro prior to this with no issues.

I have the same issue where the screen keeps flashing BUT I'm only experiencing it on the two USB ports on the right side of my 16" MBP. If I plug the screen into one of the ports on the left side of my MacBook then it works fine.

Maybe that is a temporary workaround that helps some of you. I hope this issue will be fixed soon!

Seems to be explained here: https://discussions.apple.com/thread/251012951

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

Well....same here, the external monitors are now working but if I let it sleep for a few hours the MacBook crashed every time, here are the logs when it crashed with all my apps running:

(See "logs" at the bottom of the message)

Here are the logs after I it crashed with all apps closed (I closed all apps in hopes it was a glitch with an app and one of the apps was causing it to crash, but no such luck....again the logs with all apps closed:

(See "logs" at the bottom of the message)

APPLE PLEASE HELP❗️

This is craziness that we now have to disable the sleep feature yet again, probably for another 3-4 months before

10.15.5 comes out . Hopefully after 10.15.5 this will all be over and this thread can be done and RESOLVED!

If anyone has a fix for keeping sleep enabled and to stop these crashes please post. I have not even tested with sleep off yet, just hoping disabling sleep will stop the crashing!

Same here. Running latest Catalina

• Connecting to external display results in exchange of endless flickering dark blue between the macbook and the displays (Apple thunderbolt monitor)
• Opening the macbook lid to wake it up while being connected to the display, results in the same kinda dark blue screen on the macbook with no way to move past it

Only restart helps :(

I am having the same issues with my MBP 16" and an external 4K LG screen connected using the Apple Multimedia HDMI adapter as well with a Caldigit TS3 hub.

Issues are varying, however, but seem to be related to waking up from sleep:

• Sometimes, internal screen flickers on and off, external screen dead. Can only be resolved by unplugging external screen and rebooting
• Sometimes, external screen is not detected at all, remains dead. This can sometimes be resolved by using another port on the Macbook, but this doesn't always work
• In most cases, a reboot with attached external screen resolves the isssue

I opened a support case with Apple support. So far, they suggested:

• Resetting NVRAM
• Resetting SMC
• Removing all windowserver plist files in Preferences
• Starting in Safe mode

They also suggested uninstalling CleanMyMac - which I haven't done yet because I cannot see any possible interference or explanation why a reboot fixes issues.

The case has been escalated now. I will keep you posted about the outcome.

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? 😃

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

The workaround I have found is to manually put the computer to sleep each time I leave my desk. If it auto-sleeps, it crashes if connected to an external monitor. In order to prevent auto-sleeping, I've set the auto-sleep timers to hours, so that it lowers the chance of it happening. Because I've gotten used to this, I've avoided crashes. It works, but it's still a workaround, and I don't like the fact that if I happen to forget to put my computer to sleep manually, my choices are either an unsecured computer for a few hours or a crash.

Like others have said, I am astonished that Apple has not issued a fix for this yet. I'm no engineer, but it doesn't seem like the kind of problem the (ostensibly) most cutting-edge tech company in the world couldn't fix fairly easily. It would obviously be in their interest to do so.

One can logically deduce, then, that there is something going on. It's either:

• they aren't aware of the problem, which doesn't seem probable or even possible
• they are aware of the problem and haven't prioritized fixing it, which seems irresponsible, so why wouldn't they
• or
• they are aware of the problem and it is a symptom of a deeper underlying problem that they won't acknowledge because it's not in their interest to do so

So I'd love to know which it is. Of course maybe it's something else. But come on. This is ridiculous. Fix the **** problem or at least tell us why it can't be fixed, and own the mea culpa.

I also noticed, after installing 10.15.4, that the external display I have (LG 27") suddenly had switched over to a very vivid color tone. Tried playing around with it to no avail. Did a little research, and discovered that the new "High Dynamic Range" checkbox (see screen shot) seemed to be the issue. By unchecking it, the color has gone back to normal. (Disclaimer: I'm not a graphics pro, so I don't really know much about this, and maybe someone who does understands more about it and can tell you how to use the setting properly. I'm just telling you that for a layman user like me, unchecking it fixed the problem. :)

Please see my earlier response. The new 16 inch Macbook requires more power than the LG display can supply. I solved this by keeping the 96 Watt power adapter that comes with the Macbook plugged in along with the USB-C cable from the LG 5K display. I have not had a single problem since.

I have the exact same symptoms. I've tried switching usb c ports for the monitors and disconnecting all external usb devices but it still happens. It's making the new macbook unusable without having to power cycle every time.

Plus there is no way to downgrade to mojave which at least is an option for others who upgraded to Catalina.

Apple support please look into this as a high priority.

TIA.

Same issue for me... the MacBook Pro doesn't recognize that it has the display connected to it (LG UltraFine 5K Display). This is usually when it wakes from an extended sleep. I have to restart the MacBook Pro, disconnecting and reconnecting the cable doesn't seem to help. It is connected via the Thunderbolt 3 cable that came with the display (uses one cable to charge and feed video). I have the display set as my primary display with menu and the MacBook Pro is the secondary display. Prior to this display I had the original Apple Thunderbolt Display that I connected with an adapter. Same thing was happening, so I thought it was the display and adapter, which is why I purchased the new display. I also changed the cable to the shorter Apple Thunderbolt cable because the LG supplied cable was too long.