MacBook Pro 16 external display issues

to get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences

so try doing some of those things and see if the display comes alive.

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attention to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your display more responsive.

Some displays include their own private "sleep" settings for the display alone. This can allow the display to enter its own sleep mode, on top of the Mac's not sending it data. A display that is sleeping on its own cannot respond to the Mac's query, and will stay dark.

Exactly the same issue I am facing! I have tried everything I can find online. Nothing has worked so far. Currently I am using an OWC Thunderbolt 3 Dock to connect the monitor. This seems to help a bit in the frequency of the issue but didn't solve it.

I have the same problem. One thing I tried that helped was to set the primary display as the display on the MacBook Pro rather than the external display. This has greatly reduced the frequency of the wake from sleep issue for me.

I am having the exact same problems as you (gablebt) and ahmedfromsingapore, wherein the external display simply is not detected upon waking the MacBook Pro 16" up from sleep.

I'll try Grant's suggestion below and report back, but this does appear to be a problem with the new MBP, because the same adapter, cables work with my old 2015 MacBook. Changing adapters, cables and monitors did not help.

While our symptoms are slightly different from what was described in mamrotek's original post, they seem to be very related in that they all involve the new MBP 16".

I have the same problem. I have tried 2 different USB-C Hubs and on USB-C to HDMI adaptor plugged in to my 2019 MBP 16 inch and each of them have had problems where after sleep, (this is not every time, just sometimes or after the machine has been on for a while) neither screen will come up, or just flash off and on. As of now this has been only when they have been attached to the left side USB-C sockets. When I move the adaptor to the right side the screens are able to connect, or if i reboot the MBP it will work again from the left side.

Just an update, and wondering if anyone else has noticed the same.

I have had my external monitor attached using the adaptor via the right side USB-C sockets and I have not had the same issue as I have had when it was attached to the left side.

Yeah, I think it's a major issue. I went for a few weeks and did not experience it, and then it came back with a vengeance. After the computer sleeps, it won't reengage the external monitor. Happens with two different monitors. One with Thunderbolt support, and one USBC to displayport. When it happens, I either restart or just have to use laptop only if I don't have time to restart. This is a HUGE Macbook Pro 16 problem I wish Apple would acknowledge and test for.

Another issue: When I have my thunderbolt display attached and I go into Time Machine, scroll back a few days, and then click cancel, the dock moves from the Thunderbolt (primary) to my laptop screen. Happens every time. Something is wonky with how Catalina is detecting monitors.

I have the same deal. Brand new MPB 16 and a LG external monitor. Went and got a better HDMI adaptor/cable with beaucoup shielding because the first one kept losing signal due to RF interference (and also wonking out the mouse - it'd skip to the point of being unusable). It was so on-edge that sometimes me just standing up would be enough to drop the external monitor. Better shielding fixed that.

Anyway, every third or fourth time I wake it, it can't find the external monitor and the main monitor is black, but flips on for 1/2 a second every 3 or 4 seconds as it tries to find the external screen. Everything thinks it's running properly - the touchbar lights up according to what apps are running - you just can't see a **** thing. It never leaves this state until I unplug the HDMI. Then the main monitor is detected and things start running properly. But ...

The settings are trashed. It's reverted to default settings. Sometimes the Night Shift settings vanish in the case. Sometimes the Color Profile is screwed up and has to be re-selected (even though the proper setting is in the panel). Sometimes the TrueTone settings are hosed and you have to sleep/wake again to get it back.

Even when it wakes properly, half the time the external monitor didn't wake before WindowServer resumed, so all windows I had on the external are now on the internal. So I gotta move things back to where they were. I got DisplayMaid to help with this, but since I use workspaces, that means I have to shuffle through each one still and restore each window set. It's a royal pain - and I never had this problem on any other MBP (this is my fourth one in the last 12 years) - I'm pretty disappointed in the sudden loss of dependability as that's a big reason I pay extra for Apple products.

I don't think it's a problem in the video circuitry as this only seems to affect monitors hooked up via USB, and once everything wakes up it's rock solid all day. It's something in either the firmware or OS that handles detecting external monitors and initializing things before WindowServer starts working. If it is hardware-related, it's probably in the USB-to-video circuitry not detecting a connected monitor properly and entering some weird loop state.

Please fix this mess.

That certainly sounds like a mess. Unfortunately, readers here are other Users, and your problem is serious enough you should contact support. You can call the AppleCare 800-number of use the "contact support" link at the top of every forum page on a computer-based Web browser.

I did. But looking at this thread, and others around the 'Net, it looks like there's an issue with the new 16" model and external monitors. I'll probably register another ticket with Apple on Monday in case it does turn out to be hardware and I'd be entitled to repairs or replacement.

When I called I was escalated to some "special" support and the guy was actually very helpful. We repro'd the problem and he got some logs and opened a case. That was 02/28/2020. Nothing has come of it yet, but I sense they are aware that this is a serious issue. In the meantime, it's driving me nuts and I regret "upgrading" to this new machine. Apple's software QA has gotten so bad that I rarely take a major OS update immediately anymore. Hardware seems to be the in the same boat.

Same here. When I called in the tech tried to be helpful, but seemed unaware that many people were reporting issues online. Or maybe he was told to deny knowledge. Who knows?

FWIW, one thing I've found that's helped is that the problem seems less severe if I plug the HDMI into the port on the left side, where you'd normally put power in. Maybe it's because there's less RF interference since I have my external monitor on the right, or maybe the circuitry is different. Again: who knows?

Once things start acting up, I have to reboot within a day or so. Otherwise sure enough I'll open the lid and the machine will be black-screened and need a hard reboot.

I'm beginning to suspect this is a combination issue. Part is the OS not discovering monitors in a reliable way. And the other is the USB-C stuff has some glitch when it comes to pushing video through it. In hindsight, I should have waited six months to avoid these teething problems with a new Apple product.

(And I won't even get into how the font-smoothing is screwed up on many external monitors ... how can you release a high end product and have this?)

Had the same problem with a couple of external displays (Dell, Sceptre) making the laptop flicker/cycle (volume/mute constantly blinking). Moving my USB-C to HDMI adapter to the right rear side usb port solved the issue.

I appreciate the reply but it is NOT just RF interference. When my machine starts having problems with detecting monitors the Display prefs get hammered (lose color profile, True Tone won't switch on or off, etc.). The next escalation is the system won't boot until I unplug the external monitor. The next escalation is a black-screen and after I hard reboot all my Notification Center widgets are out of order. Something is getting very confused in the OS.

I at first thought moving the HDMI connector, and getting a mega-shielded cable, had fixed things. And it did fixed the external monitor shutting off intermitently. But this other stuff still happens. It takes a couple days before things start going sideways, but the more often I sleep/wake the machine, the more likely it happens.

I plan to call into Apple Tech Supt again next week to register my findings on this. Something is definitely wrong and it's clearly affecting a lot of people.