Issue with LG UltraFine 5K Monitor After macOS 15.0 (24A335) Update

Hello,

Since Sequoia, my Mac Mini M2 Pro cannot use speakers, microphone and Camera of my 27 LG Ultrafine 5K. Hope Apple or LG would find a solution, luckily mage is visible.

Have you powered off the LG display and the 2019 MacBook; disconnected the TB3 connection; reconnect the TB3 cable; power onthe LG display, and then boot the MacBook Pro?

I would suggest contacting LG but that would be like talking to a tree…

The maximum allowable length of the ThunderBolt-3 (or-4) cable to support a high-end display under recent versions of MacOS is strictly limited to 0.8 meters for highly-engineered Apple cable, and 0.5 meters for Brand-X cables.

If you exceed those limits, the display is extremely likely to error out and go dark at full resolution.

(It may still work if set to lower resolutions below 4K, because that data rate is lower and less error-prone.)

I have the same issue. Reported to apple support who’ve replicated the issue internally.

And now they’re seemingly fixing it. Meanwhile our monitors are paperweights. Which is annoying but I guess at least they’re aware?

I have an LG 32UN880-B 32-inch 4K display connected to an M2 Mac Mini Pro (Sequoia v15.0.1) with a high-quality Belkin HDMI 2.1 Ultra High-Speed cable. There is no Apple extended keyboard control of the display's speakers as they must be enabled/disabled via the display's manual toggle. Since that is a PITA, I just use Bluetooth headphones.

Had somewhat similar issue, download the lg screen manager check if you have any updates, my computer was in the latest software but for some reason it thoughtld there was an update available after installing macOS 15, i tried running the update and it would always fail. After about 10 attempts I was about to give up.

I unplugged the monitor from my computer (m2 mac mini), went to lunch, came an hour later plugged it back and ran the lg screen manager again, i no longer had the update request and everything else was working again.

Hope it helps.

MacBook Pro, 16-inch, M1 Max, 2021

27-inch LG UltraFine 5K Display 27MD5KA, HKN62LL/A, Dec. 2016, running latest firmware

OWC 28-Inch Thunderbolt 4 cable

After updating to macOS Sonoma 14.7.1, the video signal to the monitor started cutting in and out at every resolution. I’m continuing to have the same issue after updating to macOS Sequoia 15.1. Charging the laptop from the monitor works.

<< OWC 28-Inch Thunderbolt 4 cable >>

Thunderbolt 3 is a hardware interface developed by Intel.[75] It shares USB-C connectors with USB, supports USB 3.1 Gen 2,[76][77][78] and can require special "active" cables for maximum performance for cable lengths over 0.5 meters (1.5 feet). 

from: https://en.wikipedia.org/wiki/Thunderbolt_(interface)

Based on that article, a ThunderBolt 3 or 4 cable over 0.5 meters (about 19.685 inches) is too long for reliable use with high-end displays. One known exception is that Apple sells a 0.8 meter super-engineered cable that goes slightly further.

Update: Magic has occurred.

I plugged the monitor into a USB-C port on a Windows PC using the OWC 28” Thunderbolt 4 cable.

Result: Same problem. The video signal kept cutting in and out.

I plugged the monitor into a USB-C port on a Windows PC using the 80” cable that came with the monitor. I was using that cable with my MacBook when I first started having the problem. I bought the 28” cable to try to resolve it.

Result: The monitor worked fine.

I plugged the monitor into the front Thunderbolt 4 port on the left side of my MacBook using the 80” cable.

Result: The monitor worked fine.

I plugged the monitor into the Thunderbolt 4 port on the right side of my MacBook using the 80” cable.

Result: The monitor worked fine.

I plugged the monitor into the Thunderbolt 4 port on the right side of my MacBook using the 28” cable.

Result: The monitor worked fine. When I plugged an external drive and an Ethernet adapter into USB-C ports on the back of the monitor, they also worked fine.

during these experiments, did you leave the display powered off for more than five minutes? That has been know to solve some problems where the processor in the display gets confused.

The typical recommendation for a good reset is a quarter hour.