External Displays won't come back on

For a while this wasn't happening as much for me and now its back again, happening quite often.

I just woke the machine up and it went into the flickering routine, but luckily I had my external drive plugged in separately so it was no problem to pull the connection. I was going to restart, but instead I decided to try switching the TB connection to the right side ports, and what do you know, the external screen came right up. (Usually I connect to the left side.) As an experiment I pulled the cable and switched it back to the left side, and it went back to the flickering routine. Now it is working again without a restart, plugged into the right side TB ports.

Is there a difference between the ports on either side? For others having this problem, have you tied switching sides for the connection?

I did an update yesterday to 10.15.3 and the issue has not happened since.

However, I did also restart my MacBook while the Thunderbolt cable was plugged in. This was described as a workaround somewhere so I'm not sure which one of these was the actual cause of the issue not happening again today.

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 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.

Aggreed.

Here is the response that I got in the email.

The Engineers have stated:

This is a software issue we are currently investigating that will be resolved when 10.15.4 comes out. Also Apple has received reports of this behavior and is investigating those reports.

I have the same setup, but mine is OK for the past 2-3 days since the upgrade. The only thing I can think of trying the PROM-reset? (Some had suggested earlier to do it twice, i.e. hold the keys long enough during restart to force the machine to go through the reset cycle twice in a row...) I did it myself recently, so that may have helped.

So far so good for me with 10.15.4. I had one panic after the update where I returned to the computer and it restarted rather than woke from sleep, and it told me it had a panic once it hit the desktop.

Since then, no more panics, and the computer has woke from sleep reliably over the last couple of days. Fingers crossed. This is with my backup HDD plugged into the display as well, which seemed to make the problem worse prior.

MBP 16"

LG Ultrafine 4K

10.15.4

Now I had my first panic - must have happened over night as the Macbook Pro rebooted this morning when switching it on:

panic(cpu 0 caller 0xffffff8012a16487): "AppleIntelFramebuffer::setPowerState(0xffffff81c1bee000 : 0xffffff7f95fb4d88, 1 -> 0) timed out after 45905 ms"@/AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/xnu/xnu-6153.101.6/iokit/Kernel/IOServicePM.cpp:5296
Backtrace (CPU 0), Frame : Return Address
0xffffff9238d83b40 : 0xffffff80123215cd 
0xffffff9238d83b90 : 0xffffff801245a3c5 
0xffffff9238d83bd0 : 0xffffff801244bf7e 
0xffffff9238d83c20 : 0xffffff80122c7a40 
0xffffff9238d83c40 : 0xffffff8012320c97 
0xffffff9238d83d40 : 0xffffff8012321087 
0xffffff9238d83d90 : 0xffffff8012ac2c7c 
0xffffff9238d83e00 : 0xffffff8012a16487 
0xffffff9238d83e50 : 0xffffff8012a15d69 
0xffffff9238d83e60 : 0xffffff8012a2d2fe 
0xffffff9238d83ea0 : 0xffffff8012a14b18 
0xffffff9238d83ec0 : 0xffffff8012363545 
0xffffff9238d83f40 : 0xffffff8012363071 
0xffffff9238d83fa0 : 0xffffff80122c713e 

BSD process name corresponding to current thread: kernel_task
Boot args: chunklist-security-epoch=0 -chunklist-no-rev2-dev

Mac OS version:
19E266

Kernel version:
Darwin Kernel Version 19.4.0: Wed Mar  4 22:28:40 PST 2020; root:xnu-6153.101.6~15/RELEASE_X86_64
Kernel UUID: AB0AA7EE-3D03-3C21-91AD-5719D79D7AF6
Kernel slide:     0x0000000012000000
Kernel text base: 0xffffff8012200000
__HIB  text base: 0xffffff8012100000
System model name: MacBookPro16,1 (Mac-E1008331FDC96864)
System shutdown begun: NO

System uptime in nanoseconds: 242998906414464
last loaded kext at 56691457754401: |SCSITaskUserClient	422.101.1 (addr 0xffffff7f96af4000, size 36864)

I had the same issue last week and I have not experience it again since I updated to 10.15.3

10.15.4 is out... release notes specifically mention LG Monitor bug fix. Let's keep our fingers crossed!

I have found a work around for this issue.

So far so good, have not had the same frustrating issue for 7 days! Fingers crossed.

Go to System Preferences, Energy Saver.

Click "Prevent computer from sleeping automatically when display is off".

You will get an alert that this will use more energy...fine! You are using more energy already by adding extra monitors. Hope this helps!

Hi

This happens me everyday.

MBP 16 + Thunderbolt display.

The Thunderbolt is black. But when I change brightness, i.e fn+F1 and fn+F2 (back to previous setting) on my external keyboard it come back on.

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.

Just got my Macbook 16" back from Apple. They replaced the logic board, CPU, GPU, hard drive, memory and touch pad under warranty. So far, it seems like it can sleep and wake while connected to an external monitor for the first time while i've had it.

Unfortunately the hard drive had to be wiped to do the repair and it came back running 10.15.6, so I don't know if the positive result is due to the repair or the OS. Hoping it stays this way. I'm really frustrated at the ordeal I had to go through but relieved I finally have a functioning laptop.

I am also having this issue, posted on another forum. I took my Mac into Apple this week hoping to get them some diagnostic info, but then they just sent me back with using "Feedback Assistant" from the Mac itself at home.

One thing that seems to have helped my Mac this week in particular was quitting the "Magnet" app that I use for pinning windows on the screen at various places. Any chance you have an app that does the same? Either Magnet or Divvy for example?