10.15.6, external display problem

You can't expect to get high resolutions from either of those displays when you connect them via Analog VGA. it is simply too weak and no one is testing it any more.

If you complain long enough and hard enough, you will force Apple to revise their specs to say they no longer support Analog VGA connection. they will NOT fix this.

Both of those displays support [Full Size] DisplayPort input. you should use a cable that also converts from the computer's USB-C port to the display's DisplayPort input, and your troubles will disappear.

Apple sells this one:

Moshi USB-C to DisplayPort Cable $49.95

MonoPrice sells this one:

Monoprice USB Type-C to DisplayPort 3.1 Cable - 5Gbps, Active, 4K@60Hz, Black, 6ft - Product # 24444 - $22.24

I am sure there are others as well.

If you prefer, you could connect using HDMI, a consumer-level interface, but getting the correct cables is more complex.

I resolved it by installing this version of Display Link Manager: https://www.displaylink.com/downloads/file?id=1636 But it took a few attempts, so you may need to install, uninstall a few times. Once installed, the relevant security box was automatically checked, and I'm back 100% fine on 2 screens.

Hi there - I had the same problem with a screen using DisplayLinkManager (Asus Zen Screen) which I have finally resolved through the DisplayLink forum. This is the version of the driver to install if you're on Catalina 10.15.6 https://www.displaylink.com/downloads/file?id=1636

Are you familiar with a "Passive" vs. "Active" cable or adapter? I wasn't until yesterday.

I was told to try an "Active" adapter instead of a "Passive" one, so I did and now my external monitor is working fine.

I can't believe the issue came down to the type of adapter!

I also encountered the same problem right after upgrading the OS to 10.15.6.

I have a 2019 MacBook Pro, 16 in

I'm using an older LCD monitor with DVI output. It was connected via a Kensington dock with a DVI to DisplayPort adapter into the DisplayPort port on the dock. My intention was to be able to use two monitors with this dock. Before upgrading the OS, everything was working fine with OS version 10.15.5.

I called Apple several times but didn't get anywhere with them. So, I took my MacBook Pro and the Kensington dock to a local Apple authorized service provider. I asked them to check out the MacBook Pro and the dock and see if they could fix the issue or explain why it won't work. I picked up my MacBook Pro and dock today. I was told this is a "KNOWN" issue with the latest version (10.15.6) of Catalina. Unfortunately, the service provider said they had no remedy for me other than reverting my OS back to OS Mojave. But, I chose to stay with the current OS and work with the issue now that I know what's going on.

I was told to keep checking the support forum for news of when Apple fixes this. Who know's when that will be?

Before going to the local Apple service provider, I did a lot of troubleshooting. If anyone has any specific questions, I'll be glad to share more info.

Some standard things to try:

Reset NVRAM and PRAM

Reset the System Management Controller 

Update: After consulting this guide, I tried restarting in Safe Mode. In Safe Mode, I was able to connect the monitor successfully. I just restarted in normal mode, and the monitor is also connecting successfully.

However, it might just be fixed because I restarted (a few days ago, I was able to temporarily fix the problem by restarting). So I'll see whether this fix persists or not.

I said nothing about Apple parts.

HDMI cables are available in standard, High speed, and Ultra-high speed. Using one at resolutions beyond its certification could cause your display to perform badly, or not at all.

Dell has posted a warning that certain of its displays do not work reliably with certain HDMI cables longer than 5.9 feet.

if your displays have become mirrored, and the computed 'compromise' resolution is not very good for either display, you could end up with both displays flashing due to resolution a bit out of bounds, but almost good enough.

If you think the resolution is out of bounds, you can use Safe Mode to set it right. Safe Mode takes defaults for many things including display settings, but the changes you make in Safe Mode will "stick" in regular mode.

I received a call from Apple today (8/25/2020) with an update on this issue.

Apple now admits they are aware of this issue and are working on a fix for it. They told me the fix will come in an update to Catalina, possibly 10.15.7 or a supplemental update. No time frame was given for when the update will be released.

I've communicated with DisplayLInk tech support and they aren't able to assist with the issue.

Since Apple has stated there is a known issue with OS 10.15.6, I guess we'll just have to continue waiting for Apple to resolve this issue.

I just discovered this thread. There is another thread about the same topic, but this seems more active.

I'll state my problem:

Hardware:

MacBook Pro 16"

• 2,4 GHz 8-Core Intel Core i9
• 64 GB 2667MHz DDR4
• AMD Radeon Pro 5500M 8 GB
• 4Tb SSD

All external Displays I tried this with (all result in the same Problem):

• AOC Q27P1
• Lenovo LT2452pwC
• HP EliteDisplay E242 Monitor
• Dell U2412M
• Dell 1907FP

Adaptor I have this problem with:

Belkin USB-C to VGA adaptor (F2**037)

This Problem immediately occurred after the update to macOS 10.15.6. I had a display connected right before the update (it was working perfectly) and right after the update (that's when the problem first occurred).

This is a very strong correlation for me. The adaptor works fine with a surface book and all the above mentioned displays, which leads to the conclusion that the problem lies with the macOS update.

When I plug in a Monitor via the adaptor all connected displays and the internal display start to flicker as if they can't properly be detected. This goes into an infinity loop with a flickering pattern (internal display lights up for 1/10 of a second and goes black for 1 second).

I have tried everything mentioned in this thread including rebooting in safe mode, resetting NVRAM and PRAM, etc.

The update to 10.15.7 did not solve the problem.

Of corse I can just buy a new adaptor that supports DP or HDMI (my Belkin HDMI adaptor works just fine) but I think we all agree that this is not acceptable if I spend 6k for a laptop. I have to rely on this adaptor for presentations if there isn't a HDMI available for the projector. So I bought the apple adaptor. But no one can seriously suggest that this is a solution.

Addressing the comments that the adaptor wasn't supporting high speed transmission or a certain resolution or isn't certified. Sorry but this is nonsense. First of all this adaptor worked perfectly fine previous to the update. Second Belkin is a premium brand that supports all standards. Especially with VGA its not a problem of any speed restrictions. With 4k this might be a different story but not VGA.

I will go to an apple store next week, let's see what they have to say. I am really disappointed with apple on this one. I just expect not to bother with something like this.

Did you try it is safe Mode? did you get a picture there with the default settings?

MacOS has the capability to test the connection to the display, to determine whether the cable is adequate. If your cable is not certified for the high speed of the display, it could fail to light up.

If Apple tightened the specs on cables, that could explain why it is no longer reliable.

There may indeed be a problem with support for VGA adapters.

But using Analog VGA to displays is not good move for displays you will be using daily. VGA is an antique.

Digital displays are far better, and very affordable.