[Solved] External Display Flickering at High Refresh Rates on macOS Sonoma 14.7: Diagnostic steps and permanent fix

[Kevin Martin]

Diagnostic Hardware Specs: Mac Studio M2 Ultra | OS Version: macOS Sonoma 14.7 | Archive Source: Apple Support Community #256868973

I am running into a persistent issue on my Mac Studio M2 Ultra running macOS Sonoma 14.7.
Whenever the machine encounters DSC compression and VRR handshake failure over USB-C DisplayPort, the following diagnostic log appears in Console:

WindowServer: [com.apple.WindowServer:server] Display 0x4caf link training failure / DSC buffer renegotiation

I verified that hardware connections are intact and tested across different power sources. What is the verified diagnostic procedure to permanently eliminate this symptom?

iMac 24″ M3 (16GB) | AST 2 Diagnostic Station | ESD Workstation | Calgary, AB

Apple Certified Service Technician (ACiT / ACSP) | "Verified Apple Discussions Archive"

[Justin Cooper]

Apple Recommended / Verified Community Solution

This canonical solution was verified and marked as solved in the Apple Support Community archive.

Locking refresh rate to a fixed frequency, disabling Variable Refresh Rate (VRR), and regenerating WindowServer display plists.

Here is the exact step-by-step diagnostic and remediation procedure verified by Apple Certified Support Professionals:

1. In System Settings > Displays, set Refresh Rate to fixed 120Hz or 100Hz instead of Variable (VRR).
2. Reset display preferences:

   sudo rm -f /Library/Preferences/com.apple.windowserver.displays.plist
   rm -f ~/Library/Preferences/ByHost/com.apple.windowserver.displays.*.plist
   killall -9 WindowServer

3. In monitor physical OSD menu, set DisplayPort mode to ‘DP 1.4 Standard’ without aggressive DSC overdrive.

Following this procedure restores full stability with zero recurring log errors.

MacBook Air 15″ M2 (16GB) | Glyph Atom Pro 2TB | iPhone 16 Pro Max | Lisbon, PT

Apple Certified Support Professional (ACSP) | Commercial Photographer & Digitech

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