External Monitor Issue After macOS Sequoia 15.1.1 Update

Deleting /Library/Preferences/com.apple.windowserver.displays.plist file worked for me!

I have the same issue here. I'm using a MacBook Pro M1 with a Dell P2721Q. The issue occurs whether I use a USB-C or HDMI cable, without any hub.

The issue seems to have started when I first upgraded to Sequoia 15.1 and has continued in Sequoia 15.1.1 and 15.2.

I've tested all the steps mentioned by other users, but nothing has worked for me. I also formatted my laptop twice and took it to Apple Support, but they didn't find any issues during the tests.

I tested the same monitor and cables with another MacBook Pro M1 (running Sequoia 15.1.1), and the same error occurred. I also tested two different MacBook Air M1 running Sonoma and a Dell running Windows, and no issue occurred.

It seems the error occurs more frequently when I use the camera, watch videos on the external monitor, or perform tasks that demand more from the video adapter. During meetings with the camera on and screen sharing, if the meeting window (normally Google Meet on Chrome, but it happens on Safari too) is on the external monitor, the issue becomes even more frequent, making it impossible to use the external monitor.

Today, I closed the lid and used the external monitor as the primary display. I was on a call with myself, playing a YouTube video that was being shared, and no issues occurred. It's important to note that the camera was off since I don't have an external webcam. After some time, I opened the lid and continued playing the video without any issues, until I opened the built-in camera. Once the camera was turned on, it took a few seconds before the screen went black. The message 'No USB-C signal from your device' appeared, and after two seconds the screen returned to normal.

Same here.

I am using a LG 29UM69G-B Ultrawide Monitor as external display on my MacBook Air M1 since 2021 with no issues (connected directly via USB-C cable, no external dock for the monitor connection). MBA stays open all the time as my second screen. After upgrading to 15.1, the external display randomly goes black for 3-5 seconds, active windows on this display move to the MBA display and return after 5 seconds to the external display. Sometimes the external display has a thin red border for a second.

This happens randomly, sometimes after 30 minutes, sometimes 3x per minute, In fact it just dropped out multiple times as I'm writing this. It also continues after update to 15.2, I was hoping that this version would eliminate the issue.

I haven't changed anything on this setup before the problem occurred. After that, starting with 15.1.1, I tried a brand new USB-C cable on both MBA connectors, changed the display setting as most of you did (True Tone, refresh rate 60/75 hertz etc.), updated to 15.1.2 and 15.2, tried the LG monitors OSD options (game mode, reaction time, name it.)

I use the setup for work and need a quick solution for this problem. Hope that some Apple software engineers are taking care of this bug.

I now remembered what I did to fix the issue last time this happened after a MacOS update:

Power your monitor off and turn it on again.

Had the same problem with an almost new dell display and mac mini m2. After everything failed, I did a factory reset on the Dell and everything works again….

Good luck to all

Siggie

This is still an issue on 15.2. I've updated my M3 Macbook Air and a portable monitor that worked fined before updating via the same USB-C cable, now it only gets power (I see the monitor splash screen) but does not connect to my MBA no matter what port I try, I've tried rebooting, resetting PRAM, nothing seems to work. One time it showed the display for 3 seconds after rebooting while leaving the monitor connected and then it went black again. Also it connects fine to a dock I have that's connected to 2 monitors (via DisplayLink) and it connects to a different monitor via DVI to USB-C cable without issue, (that monitor is powered though). Maybe the issue has to do with transmitting the display signal and power via one cable, but prior to the update it worked fine.

I have confirmed this is working with my M1 Macbook Pro with the same version of Sequoia 15.2, so it almost seems like it's a specific issue with a combination of MBA M3 hardware (potentially other models too) and 15.2. I hope they fix it soon, because it's very frustrating.

Hi.

I'm using a Satechi Multi-Port Adapter 4K and an IIyama PL2792UH (4K). It appears that the screen is now correctly detected if I set the Input from "Auto" to "HDMI". I'm also back to 60 Hz. Waiting for more testing to be sure that it's a workaround with my devices.

Franck

Try connecting a iPad as sidecar display and your HDMI monitor comes back to life magically, but only as long as sidecar is active in my case.

I have been reporting this issue since month, yet every update Apple pushes does not address it.

What works for me is going back to 15.1 fresh re installation with TimeMachine profile recovery.

So far what didnt worked:

• upgrade to 15.2
• deleting displays settings files
• Reseting hardware stuff at boot
• Switching cables with or without docking station
• Reseting display settings
• Switching display frequency

MBP M1 with DP external Dell display via Dell docking station

I was facing same issue with my following config. i.e. flickering screen not detecting display

• Mac M3 pro - Sequoia 15.3
• Samsung - 49" Odyssey OLED G9

Following setting helped. and its now working as expected.

I think something is not letting GPU enough resources to work with ext displays properly. therefore I downgraded refresh rate of built in display and also turned off some other option which as per my understanding may cause resource issue.

Apple certainly needs to fix this as following is just a work around (for a $3k machine) and not guaranteed if this will work for everyone.

Try these fixes:

1. Use a Different Cable/Adapter – Test a USB-C to HDMI adapter instead of HDMI-to-Type-C cable.
2. Change Display Settings – Set a lower refresh rate (e.g., 60Hz) and try different resolutions.
3. Disable True Tone & HDR – In System Settings > Displays, turn off True Tone & High Dynamic Range (HDR).
4. Reset NVRAM & SMC – Restart and reset NVRAM (Option + Command + P + R) and SMC (Shut down, hold Shift + Control + Option + Power for 10 sec).
5. Try Different Port/Monitor – If possible, test another monitor or port.
6. Check for macOS Updates – Apple might release a fix soon.

I had this problem with my MacBook 16 inch with this upgrade. Mine would not work with usb-c to DisplayPort cables. This was fixed when I took an old usb-c to DVI cable and attached. I now have full resolution and connectivity

uni USB C to HDMI Cable 4K@60Hz solved the issue for me. I own M1 Macbook Pro from 2021. plugged USB C to macbook and HDMI side to my LG 4k monitor. Hope it helps!

It worked for me. I plugged in the monitor, and in the first few seconds when the Mac detects the external display, I set it as the primary screen — and it worked. I’m using a MacBook Pro M2 (Sequoia 15.4.1) here. Not sure if that has anything to do with the issue!

Restart your computer with the main monitor unplugged. Then plug it in, and both monitors will work until you restart.

This worked for me.