External Monitor Issue After macOS Sequoia 15.1.1 Update

After reading this thread I tried one more thing - replacing my $70 Mac USB-C to HDMI (Multiport) adapter with a much less expensive Anker USB-C to HDMI adapter and it fixed this problem. Something in Sequoia broke the mac version of this adapter, which is ironic considering it's so expensive. I also tested with a Nintendo Switch USB-C to HDMI adapter with the same results. The Anker and Nintendo adapters work fine, the disconnecting/blinking went away. Only occurs with the Mac brand adapter (MacBook Pro > Mac USB-C Multiport > HDMI cable > LG Ultrawide monitor).

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

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.

Sequoia has washed out my colors. They are so light, that anything white isn’t invisible including boxes that need to be checked. I can do a search for white underwear and barely see anything. My MacBook Air is 2022 so I got a new M3 for Christmas same thing! So disappointed in Apple. I been a Mac user for 20 years.

clarka117 wrote:

Sequoia has washed out my colors. They are so light, that anything white isn’t invisible including boxes that need to be checked. I can do a search for white underwear and barely see anything. My MacBook Air is 2022 so I got a new M3 for Christmas same thing! So disappointed in Apple. I been a Mac user for 20 years.

Is this on the internal display or external? If it is on the internal display, then your problem is completely different from what is being discussed in this thread. You should start a new thread and give details about your system, including an Etrecheck report. FWIW, I do NOT see these washed out colors in any of three macs running Sequoia (one Intel, one M1 and one M4 Pro), and this is the first I have heard of this. The fact that it happens in two macs of yours suggests that you may have migrated whatever was causing the problem from old to new.

Same here. I thought my monitor was failing but realized it happened after a Sequoia update. Flickers off for 2 seconds every few minutes, kills my audio coming out of the monitor as well during that time, which usually happens when I'm in the middle of an important Zoom meeting for work of course.

It's definitely not older hardward only. At least my issue, where it flickers for 2 seconds, is happening on a brand new Dell Ultrasharp I bought late last year, and was running perfectly fine until I updated to Sequoia. It is connected directly to the Mac (also purchased middle of last year, a Mac Studio M2) via USB C for all audio/video, and powered externally.

Data point- no issues here.

2019 Intel MBP with UtechSmart USB-C dock to Samsung HDMI display.

M1 mini with LG UltraFine Thunderbolt display and Dell HDMI display

M3 MacBook Air with LG UltraFine Thunderbolt display

All running Sequoia 15.2, all working perfectly.

I am having the same problem with my MackBook Pro and my Vizio monitor. I had a TV screen that had a defect on it and I use it as my second monitor. It has worked seamlessly for several years. No problems until I updated to Sequoia. It tells me no signal even thought shows in System Prefs and is set to correct input. I've checked cables, etc. Nothing works.

thanks for this, the usb c port swapped work for me MacBook Pro M1, os15.2 , as far as I can tell the one port thinks the monitor is 1080 max but the other port thinks it is 4k. I am using a cheap dock to do this so it is HDMI into the dock and the dock is usb into the Mac itself. swapping the dock between the ports on the Mac is what fixed it.

RESOLVED (for me, for now)

I've been watching this thread because I have had the same problem everyone else has. Here is my setup:

MBP M1Max

3 identical LG 1920x1080 monitors (27MN60T)

Main display (center) uses HDMI to HDMI

Extended displays use HDMI to USB-C

Refresh Rate: 75hz (on all three)

Color Profile: LG FULL HD

No docking station.

Because MacOS can get confused on waking and swap my 2 extended displays (its own frustrating bug that has been present for at least the last 2 operating systems), I HAD been using VGA to USB-C by way of an adaptor for 1 of the 2 extended displays. That is the screen that was blacking every couple minutes once I updated to 15.1. As I was trouble shooting I noticed that screen was fixed at 60hz refresh with no option to adjust to the 75 the other 2 used. I bought an Anker HDMI to USB-C cable assuming that as long as I was replacing a cable I would try a decent quality one rather than the least expensive.

I have been running now since Saturday with no screen black out. I have no idea if this will help others or not, but thought I would share, just in case it might.

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.

If someone gets a problem with second (and third) monitor not being recognized by MacOS after Sequoia 15.2 update you might want to check this link on reddit. TL;DR: you might need to remove /Library/Preferences/com.apple.windowserver.displays.plist file and restart to make it work again. Now Apple, pls solve this issue officially.

Sequoia 15.2 External Monitor FIX Steps:

1. Delete /Library/Preferences/com.apple.windowserver.displays.plist file
2. Empty trash bin
3. Shut down MacBook (not a restart)

I use a LG Ultrawide as a second monitor. Works perfectly fine again now. Good luck! My Applr Rep had no idea until I found this from a Reddit user.

Nope, didn't work for me.

"I have the same issue. The workaround is to power the monitor first with its own power supply and then connect the video (usbc or hdmi). Power and video delivery over 1 usbc cable seems broken."