External Monitor Issue After macOS Sequoia 15.1.1 Update

Same here, LG 4K second monitor connect to MacPro, flickered for a few days, now doesn't work at all. Mac won't recognize or connect with it.

Until 15.4. Release Candidate (latest), there is no change for me

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 was occasionally detecting the monitor till now but now it just doesn’t… It’s hilarious how Apple Support doesn’t even acknowledge this issue. Won’t buy another Apple product for real after this.

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

This worked for me.

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!

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.

Since two days my primitive graphics adapter works well. Your link, TxPomeroy, wasn‘t helpful for me as Amazon unfortunately doesn‘t deliver it to Germany.

I‘ll await 15.1.2 now, in the hope, Apple will repair this bug soon…

Thanks for this! Quick question: are you only running one external monitor, and not multiple? I was able to run 2 before, and with the update, now only one works, and only one is detected by my mac. No issues with my DELL windows laptop.

Having the same issue here, there is a dead zone on my external monitor, upper left corner, where clicks just don't register. Can't tell you how frustrating and time consuming it is to have to move a toolbar or window just to click.

Running a Macbook Pro 2021 with an apple USB-C to HDMI adaptor for an ASUS external monitor.

Checking daily to see if there's a software update.