External Monitor Issue After macOS Sequoia 15.1.1 Update

Exact same issue for me as OP. After updating to Sequoia 15.2 (I don't recall what the previous version was), the flickering issue occurred immediately after the update. Nothing else has changed about my set up after the update, so I feel very confident that the 15.2 update is the root of the issue.

Here's my set up prior to Sequoia 15.2 Update:

• Macbook M1 Max, 16-inch, 2021
• MacOS Sequoia 15 (not sure which previous version)
• External displays:
  • Working normally: "Display 1", LG 27GN650-B (connected via HDMI port)
  • Malfunctioning, flickering: "Display 2", LG 34UM69G-B (connected via usb-c port, USB-C to USB-C display cable)

Steps that failed to resolve issue:

• Follow steps 1-4 outlined here. Did not resolve issue.
  • Unplug cable and monitor power cord
  • Mac is already at latest update
  • Restart Mac
  • Change color profile of external monitor to Color LCD
  • Change refresh rate to 60 hz
  • Disabled true tone/night mode where applicable
• Changed USB-C cables, and tried plugging USB-c cable into different USB-c ports. Neither resolved issue
• Swapped display cable from USB-c/USB-c to USB-c/DisplayPort. Did not resolve issue.

Steps that resolved the issue so far as of Dec 19, 2024 at 11:06:

• Swap display cables between Display 1 (working) and Display 2 (malfunctioning):
  • Display 2 is now connected via HDMI cable to mac HDMI port
    • Color profile: Color LCD, 60 Hz refresh rate, no true tone/night
  • Connect Display 1 via DisplayPort to USB-C mac port

Since swapping display cables between external monitors, the flickering has stopped. I will update accordingly if anything changes.

Update Dec 19, 2024 2pm: Unfortunately, the flickering still occurs but it's less often and less intrusive. The flickering happens maybe once an hour. And, instead of my mac thinking the display has been disconnected and rearranging all my open windows, it's just a brief off/on flicker and no windows move.

I suffer the same issue after upgrading to 15.2 (most probably from 15.1, where everything works fine) on a MBP M1 2020, connected to USB C hub with power + external display via display port + USB stuffs.

What I have done so far to solve this issue in this order (actually I don't know which one as an effect):

• ensure the 'Prevent automatic sleeping on power when the display is off' setting is enabled
• configure the MBP display as main, and switch it back to the external display
• reset the Amphetamine App settings to default, then in settings disable the option 'allow system sleep when display is closed'
• switch external display refresh rate from 120 to 160: it makes the external display not working at all, even after a reboot
• disconnect the USB C cable (external display + power)
• shutdown
• reset (or try at least) SMC and NVRAM/PRAM
• reboot

Then it finally works again when the display is closed \o/

I suffer the same issue after upgrading to 15.2 (most probably from 15.1, where everything works fine) on a MBP M1 2020, connected to USB C hub with power + external display via display port + USB stuffs.

What I have done so far to solve this issue in this order (actually I don't know which one as an effect):

• ensure the 'Prevent automatic sleeping on power when the display is off' setting is enabled
• configure the MBP display as main, and switch it back to the external display
• reset the Amphetamine App settings to default, then in settings disable the option 'allow system sleep when display is closed'
• switch external display refresh rate from 120 to 160: it makes the external display not working at all, even after a reboot
• disconnect the USB C cable (external display + power)
• shutdown
• reset (or try at least) SMC and NVRAM/PRAM
• reboot

Then it finally works again when the display is closed \o/

Curious, how many hours passed without this issue manifesting? Using the same docking station, I've had a full 8+ hours with no issues before it started manifesting again.

Curious, how many hours passed without this issue manifesting? Using a similar docking station, I've had a full 8+ hours with no issues before it started manifesting again.

I haven't that issue until upgrading to 15.2 on my MacBook Pro M1. Now the system doesn't see my external monitor connected via DisplayPort. Very disappointed.

When can we expect a fix? It's already been weeks.

Update: Checked on my wife's Mac Air M2 and hers works fine and she is running Sequoia 15.1.1. She has a different and newer brand of USB-C dock but still just one of those small USB multi-port docks with a couple HDMI connections and a couple USB connections. Nothing too fancy or expensive. Mine is a bit older but, again, no issue on Windows laptop.

UtechSmart USB C Docking station model UCN 3270-2

Bought back in October of 2021 off Amazon

It worked fine until this morning. Not sure when OS got the update but haven't used the mac in a few days since use Windows laptop for work and that's most of my time.

I updated the DisplayLink driver on my mac from the Synaptics website and restarted but still not fixed. Maybe there is somewhere better to get the driver from?

The cheap little dock on my wife's mac was bought August of this year and works fine on both our macs. So, naturally, I'm highly suspicious of my docking station and have ordered a new one.

BTW, thanks for the help. It's greatly appreciated.

Happy Thanksgiving!

I've the same problem on my MacMini M1 with two LG 34" monitors. One of them, connected by an USB-C/Thunderbolt to HDMI adapter cable, gets dark for 1-2 seconds every few minutes since updating to 15.1.1.

When I changed the refresh rate to 30 Hz, then BOTH monitors showed this behaviour, surprisingly simultaneously!

Another USB-C to DVI to HDMI adapter chain didn't help. Looking for some other hardware in my junk box, I found an adapter box for VGA, DVI and HDMI. Using HDMI again, both monitors are as functional as before.

Ordered a new docking station/KVM for my Mac Air M2 and now all is back to normal. I run with an external mouse, keyboard, camera, and monitor and close the Mac up to switch between work Windows laptop and my personal mac. I don't know that there are any DisplayLink updates in the 15.1.1 update but my issue started about that time. Or, seeing as how the older docking station didn't have any sort of heat sink and just ran blazing hot all the time, it may have just been on its last legs. Regardless, haven't had any issues since using the new docking station so I'm happy now. If you're interested, here's the link to what I got on Amazon:

https://a.co/d/c8BC06S

There are a lot of these things out there, but this had just enough USB ports and the one HDMI port. No more issues for me. Hope this helps.

Can't really say for sure, maybe a couple of days after the update that I noticed the issue. I don't spend a lot of time on my Mac during the work week. I'm mostly on my work Windows laptop until the weekend so I didn't plug it in to the Mac until a few days after the update. Plus, I didn't spend a lot of time troubleshooting. I plugged the old dock back into my windows laptop after the issue started on the Mac and all seemed fine. In the end, I can't really be sure it was the dock or the Mac update. All I can say for sure is that the new dock works fine on my Mac. So, I'm happy and it ends there, for me at least. This may not be the solution for everyone, but it may be for some.

Hours later, using the simple adapter from my junk box: one single event only.

Interesting that the box became a bit warm in the beginning, then it cooled down and stayed cool. Perhaps I should try the original adapter again ...

hi TxPomery that link to Lionwei is interesting but you say it has one HDMI port - I see two, do you use displaylink to overcome lack of MST , I am looking into an adapter for my M1 macbook air and want to use 2 or 3 external monitors displaying separate video , your link looks good but all these stories of flickering with mac OS updates sound a bit familiar - windows doesn't deliberately lock out functionality the way mac OS seems to

Yeah, it has two HDMI. Sorry if I gave you the wrong impression since I only need or use one. But, the Amazon listing shows you can have two external monitors but they'll show the same thing. Not a problem for me since that's all I need. This seems to have been a limitation of Macs for a long time. Even my 3 year old KVM/dock had the same limitation. I haven't used Macs long enough to know how you can get around this limitation. Good luck.