External Display Issue on macOS Golden Gate 27 Developer Beta (M4 Pro)

Community Apple Developers
Andrew_Jester OP
Created 2w
Replies 4
Boosts 0
Views 319
Participants 3

Hello everyone,

I am currently running the macOS Golden Gate 27 Developer Beta and am experiencing an issue with external displays.

I am only able to connect one external display successfully. Any additional external displays I try to plug in do not work or are not recognized by the system.

Here are the details of my setup:

Mac Model: 16-inch MacBook Pro (Apple M4 Pro, 24 GB Memory)

macOS Version: macOS 27 Version 27.0 Beta (Build 26A5353q)

Displays: Two LG UltraFine 5K Thunderbolt displays

Connection Type: Connected directly using two separate Apple Thunderbolt 4 cables

Troubleshooting steps already taken:

  • Restarted the Mac

  • Tested different cables and ports

  • Verified both displays work individually (only fails when both are connected)

Has anyone else encountered this issue on this specific beta build? If so, have you found any temporary workarounds?

Side note: Feedback Assistant was not working for me. I tried it in the Web, and the native App, neither of them would work. I am posting here because there was nowhere else to submit this bug report.

Replies  4
Boosts  0
Views  319
Participants  3
Automatt26 OP
2w

Having the same problem with a 14-inch MacBook Pro (M5 Max)

Two LG UltraFine 5K Thunderbolt displays

Only one will work at a time, no matter which ports are used.
nphowe OP
1w

This is really encouraging to read.

I had a MacBook Pro with M4 Pro that I had upgraded to macOS 27 DB1. Last week I was given two LG Ultrafine 5K displays and I could not get them both to work using my Dell WD19TB dock. By happenstance, I had already ordered a new WD25TB5 dock and a MacBook Pro with M5 Pro, so I thought surely I’d be able to use Thunderbolt 5 to take advantage of the bandwidth needed to drive two 5K displays. But they still won’t both work, connected to the new dock or directly to the new MacBook using ports on opposite sides of the laptop. I get one display, generally whichever gets plugged in first, while the other gets detected as a Thunderbolt device but not a display.

Notably, the new MacBook needed to get upgraded to Golden Gate by Migration Assistant, so I never tried these two displays with Tahoe. Also, when I connect the dock to my Windows laptop (Dell Pro 14 Premium), both displays light up beautifully.

I think there are issues with the Golden Gate thunderbolt stack.
nphowe OP
1w

I wonder if this is the issue I’m running into: https://developer.apple.com/documentation/macos-release-notes/macos-27-release-notes#Thunderbolt
nphowe OP
6d

I just updated my MacBook Pro (M5 Pro) to macOS 27 DB2 and connected to my dock. All good now!

External Display Issue on macOS Golden Gate 27 Developer Beta (M4 Pro)
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