External Monitor Issue After macOS Sequoia 15.1.1 Update

Thank you for sharing that thread and the fix! This finally fixed it for me. My workaround was using a dongle and connecting via HDMI (for display and USBC just for power) instead of USB-C only (how it used to work). Now I don't need the dongle and HDMI cable anymore. Question is, why can't apple patch this? 🤦‍♂️

I had the same issue. It recognized one of my external monitors connected via HDMI, but not the one connected via DisplayPort. I tried swapping cables, went so far to buy a new docking station that had HDMI only connections. Nothing worked. Tried deleting a plist that was suggested. I found a reddit post that linked back to another discussion and they mentioned unplugging the power cord from the monitor, leaving everything else connected. I just did that and my 2nd external monitor is working again!!!! Hopefully it helps others. This is the post that led me to it: https://www.reddit.com/r/MacOS/comments/1hc8mcz/comment/m22ql12/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

There is no doubt that this problem has a serious impact on those affected. But, since it does not affect everyone and, in fact, it seems to affect only a minority of users, it seems futile to expect that a software update will fix it. Instead, you should try the solutions offered, particularly the deletion of windowmanager preferences.

I accidentally fixed my issue. I shut down and restarted in safe mode. The external monitor seemed to work using USB-C. So I shut down and restarted. And now it works fine. I didn't change anything or do anything differently. Just the safe mode restart. I am not sure if this is a fix, but it worked!

Just updated to Sequoia 15.3 (about 30 minutes ago) and the same problem, described above, just occurred again. Was writing an email and while I was typing, my computer went to sleep and i had to log back in to get back to work.

I don't know but that seems to be a really big bug to just let pass like that for all this time (I mean Sequoia 15.1 is out since October last year !

Same here. I waited 4 generations to make sure I get a product that has virtually no catastrophic problems like this. Seeing how this thread is flat out ignored, it is not too hard to determine Apple is more concerned with looks than usability. I took mine straight back to the store for a refund less than 24 hours after I bought it. Spent over a thousand dollars on it. Downloaded and installed irreversible system update and my left monitor stopped working.

Remember when the company was run by a visionary man who cared about user experience? Yeah... me too.

I have a MacBook Pro 14" (November 2023, M3). After updating to the latest macOS Sequoia, it was working fine until I connected it to my Samsung monitor via HDMI. The computer restarted on its own and then completely shut down. Since then, it has been unresponsive—no signs of power, and the charging cable does not light up at all.

It is dead.

Experiencing exactly the same: iMac 2022, external display via DVI/Thunderbolt. Ran for 3 yrs without any problems, after updating to 15.3 yesterday all went down. Ext display constantly switching off for ~5sec and on again after. Follows no logic, happens occasionaly every 2 mins, then 1hr everything is good. Tried every described solution, nothing changes.

Is there any chance that someone from Apple comes accross this discussion and does sthg against it?!? Work is almost not possible like this

Solution for me (Problem solved):

macOS 15.3:

I bought a new USB-C to HDMI cable and now it's all fine! Connected directly to the Macbook's USBC port, no hub.

No screen failure, no "blackouts" for three full working days.

I don't know if this works for everyone, but it is worth a try.

Unfortunately, my USB-C to HDMI cable from UNI had been the first one that showed the problem. With every Sequoia update I do try that one, up to now without success. I tried three other hub adapters, only one of them works, but only at 30 Hz ... disappointing.

So, dear Teichfrosch, which adapter do you use now?

My impression is, that the UNI adapter gets warmer than e.g. with Sonoma, but not sure...

I run trivia at a few places, and last night, I got my M2 Air to connect to TWO external monitors (huge TVs, both Samsung) on an HDMI splitter. I fiddled with the settings for a bit, and what worked finally was dropping the refresh rate from 144Hz to 60Hz. I came home and tried the same M2 Air with a KYY external, but nothing (although the same small KYY monitor works on a Dell). I hooked all three of my desktop monitors, a Dell, a Samsung, and an Acer (one at a time) to the M2 Air, and ALL worked with no adjustments to the refresh rate. So I started thinking it was the cheap KYY, but others in this discussion cannot connect with high-end monitors (yet I could last night and today). Frustrating.

To add to all of this, my new M4 mini connects to all three desktop monitors (again, a Dell, a Samsung, and an Acer), but the Dell (and ONLY the Dell) will go black for 3-5 seconds then come back on at least 5 times in an 8-hour workday.

Is Apple going to address this time-wasting ****???

Thanks for the input, Luis, but your statement has a few glaring logical failures. "But, since it does not affect everyone and, in fact, it seems to affect only a minority of users..." While almost certainly true that not "everyone" is affected, to follow that with "in fact" is problematic, as you then identify that this problem affects "a minority of users;" but how do you know that to be true? Are you basing that on this discussion? If so, then wouldn't you need to know how representative this group is of the population of users to determine a "minority?" Since this is a self-selecting group you cannot infer anything about the representativeness of this sample compared to either the sampling frame or the population (quite the opposite; this group is likely very unrepresentative of the larger population). Further, you stated that "it seems futile to expect that a software update will fix it." Really? So you're assuming that a computer company does not fix bugs? What is that statement based on? My point here is that this thread is ongoing to try to figure out the issue and hopefully get Apple to fix it. Adding jump-to-conclusion offerings that breakdown into logical fallacies immediately is no help at all.

@AppleSince_85 - nice name! I too started using Apple in 1985, by the way.

I am not diminishing the trouble that this problem causes to all those affected.

Debating what is and is not representative is futile, so let's just agree to disagree on that - neither of us has data to formally claim, one way or the other, it is a matter of point of view, so I retract the "in fact" comment.

I hope that it gets resolved, and sooner rather than later.

Thanks Teichfrosch, I ordered that cable and will report. It seems to be similar to my UNI cable (I bought it in 2020). Same price, but might be a newer generation.

Yesterday I got another hub type adapter (the forth one), it seems to work too. But I would prefer an adapter cable.

Same issue on Sequoia 15.3.1, using 4 different USB-C -> HDMI hubs or cables.

My monitor was not detected anymore after macOs upgrade from Sonoma. This monitor works on a PC with same USB-C devices.

After reading all the comments and reports, I wiped my mac and reinstalled Sonoma 14.7.4 (latest to date). Issue vanished.

What a shame, Apple.

I won't upgrade until I read a public statement from Apple saying the bug is fixed.