External Displays won't come back on

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.

Well I think I might of found some kind of Fix, I unplugged everything from the Mac, did a PRAM reset, restarted the Mac after the reset, without plugging in anything, then shut down the Mac.

I then restarted the Mac with the monitor plugged into the first USB port on the left side of the Mac, and I have not had a problem in about 3 weeks. I have let the computer go into sleep mode, logged out, and put the Mac into sleep mode manually, and all works fine.

Hope this helps.

I think I may have stumbled across a solution. I was having this problem with my LG 5K Ultrafine display and my new MacBook Pro 16. I never had a problem with my previous 15 inch MacBook. I'm running macOS Catalina version 10.15.4. I noticed that the LG shutting off was accompanied by increased fan speed on the MacBook. I tried plugging in my standard power adapter that came with the MacBook. The display has been stable since. I think the MacBook was demanding more current than the LG display could provide in its charging circuit and this was causing the LG to disconnect and re-connect. The MacBook is either charging from the power adapter or taking charge from both it and the LG display.

After replacing the logicboard (which nowadays also includes RAM, HDD, and... well, everything) my computer still had the same old crashes anytime it went to sleep with an external screen connected.

However, after updating to 10.15.6, I've been connected to the same screen (and puting the computer / allowing the computer to sleep all the time.

I've not had a single crash!

For me, 10.15.6 fixed the issue. If it's because of a COMBINATION of a new logic board AND 10.15.6, I cannot say.

For those of you still stuck with the problem - I feel for you. I hope something further down the line fixes this.

P.S. This article had some good info in the comments:

https://mrmacintosh.com/10-15-4-update-wake-from-sleep-kernel-panic-in-16-mbpro-2019/

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

I think I found one solution to the problem, and that is use the right side USB ports on the MacBook Pro for the Monitor connection, I am doing this at the moment and the Mac wakes up both monitors without any problems, but I still get the brightness change on restart which is really annoying.

I've got feedback from Apple Support (Thank you!). This is something that they are working on a fix via software for. It is slated to be part of the 10.15.4 release is the information that I have received.

About a week since updating to OS X 10.15.4 and so far so good. LG 32" monitor works after sleep, plug/un-plug, etc. Computer gets warmer than I'd like while connected to the monitor but temperatures appear to be within Apple defined tolerances (per Macs Fan Control).

I have too second this... I was having issues where the LG screen stayed black after trying to wake from extended sleep. The MBP display would flicker and the only way to resolve was a restart. I noticed increased fan speed as well. My setup has been stable for a while now (since 10.15.3) but I think because I am using the MBP supplied power brick and not drawing power from the monitor. One reason I did this was because I noticed a battery drain when using the monitor as the power source under a heavy load (where the fans would rev up). The battery drain has been fixed by this as well.

I've been monitoring this thread and having same the problem. For what it's worth, I did the same thing Tom D. mentioned; plug my MBP power adapter into the MBP. Don't know why, but it solved my problem. Hope it helps others. Thanks Tom!

SOLVED! I've got the motherboard replaced. The macbook went to sleep while being at lunch, came back, and it started up just fine. But, depends if the issue reoccur after a while. If so, i'll let u know. But for now it's fine.

Yes! It seems to have resolved with 10.15.6! I just tested it by setting my display to go to sleep after one minute of inactivity. I let it go to sleep, waited a few minutes to be sure it had totally gone to sleep, and then tried waking it. For the first time since I started using the MBP 16" with my LG external monitor, the wake-from-sleep problem did not present. (I have been doing only manual go-to-sleep for months now--that was the stop-gap solution.) I'll keep an eye on it to see if it happens again, but this is the first sign of success I've seen yet.

I had the same issues. After updating to 10.15.4, I returned all my setting to normal and have had no issues.

With 10.15.6, I am no longer having the issue.