External Monitor woes with Tahoe
As the title says the native buttons are no longer working with controlling monitor volume.
I have tested multiple cables HDMI, USBc(thunderbolt4), USBc to HDMI, USBc to Displayport.
I have tried on 3 separate monitors that I have 2 different LG 4k monitors and a USBc Hub LG 5k2K ultrawide.
All previously worked just fine and now none of them are. I have tried clearing caches/temp files etc. Sometimes the monitors just straight crash black screen when I try to play videos. Sometimes when they crash they keep crashing.
Here is a more in depth summary of everything
System:
- MacBook Pro M2 Pro 2023
- macOS Tahoe 26.5
- LG HDR 4K monitor x2
- LG 5K2K Ultrawide
- Thunderbolt 4 dock + direct monitor testing
Problems:
- External monitor randomly blacks out for a few seconds
- Monitor beeps during blackout/reconnect
- macOS session stays alive underneath
- Lost native macOS volume control for monitor audio
- HDR makes instability significantly worse
- At one point display renegotiated to only allow 4K30
- BetterDisplay/MonitorControl DDC commands can destabilize display
- Setting brightness to exactly 100% through DDC can reproducibly trigger blackout/reset
Scenarios tested:
- TB4 dock → monitor via HDMI
- unstable
- blackouts
- audio issues
- DDC weirdness
- Direct Mac HDMI → monitor using LG supplied HDMI cable
- same behavior
- USB-C → DisplayPort direct
- same behavior
- Portrait + landscape
- both tested
- HDR instability occurs in both
- HDR OFF
- more stable
- HDR ON
- instability increases dramatically
- triggered repeated display resets/blackouts
Things ruled out:
- Multiple cables tested
- Dock bypassed entirely
- No GPU panics found
- No AGX crashes found
- No kernel panics tied to display events
- Internal MacBook display remains stable
Terminal commands used:
Check for panics:
log show --predicate 'eventMessage CONTAINS[c] "panic"' --last 7d
Search for GPU/display related issues:
log show --last 7d | grep -Ei "panic|AGX|GPU|WindowServer|watchdog|IOGraphics"
Live display negotiation logging:
log stream --style compact --predicate '(eventMessage CONTAINS[c] "DisplayPort") OR (eventMessage CONTAINS[c] "HDMI") OR (eventMessage CONTAINS[c] "link") OR (eventMessage CONTAINS[c] "sink") OR (eventMessage CONTAINS[c] "DCP") OR (eventMessage CONTAINS[c] "AGDC") OR (process == "WindowServer")'
WindowServer/display reset attempt:
rm ~/Library/Preferences/ByHost/com.apple.windowserver*
sudo rm /Library/Preferences/com.apple.windowserver.plist
sudo reboot
Important log/errors observed after enabling HDR:
Unable to render backdrop-aware vibrant color matrix filter while existing memoryless offscreen surface in use
Also observed during blackouts:
- DCPAVAudioDriver resets
- IOAVFamily renegotiation activity
- playbackDoneOccurred events
Current suspicion:
- macOS Tahoe external monitor/HDR regression
- DDC/display negotiation instability
- possible LG firmware/scaler compatibility issue with Tahoe