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[Solved] External Display Flickering at High Refresh Rates on Mac mini M4 Pro: How to resolve DSC compression and VRR handshake failure over USB-C DisplayPort

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Home › Forums › MacBook, iMac & macOS Lab › [Solved] External Display Flickering at High Refresh Rates on Mac mini M4 Pro: How to resolve DSC compression and VRR handshake failure over USB-C DisplayPort

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  • November 14, 2026 at 11:04 pm #14129
    Ann Wagner
    Community Contributor
    Diagnostic Hardware Specs: Mac mini M4 Pro | OS Version: macOS Sequoia 15.0.1 | Archive Source: Apple Support Community #256545650

    I am running into a persistent issue on my Mac mini M4 Pro running macOS Sequoia 15.0.1.
    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 0x634a 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?

    Mac mini M4 (16GB) Home Server | Apple TV 4K | Eve Energy Thread Mesh | Kyoto, JP
    Smart Home & Matter/Thread Integrator | "Verified Apple Discussions Archive"
    November 14, 2026 at 11:04 pm #14130
    Zoe Rivera
    Senior Specialist (Lvl 8)
    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.

    Apple Vision Pro (512GB) | MacBook Pro 14″ M4 Pro | AirPods Pro 2 | Porto, PT
    Apple Certified Support Professional (ACSP) | visionOS Spatial Computing Developer
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