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[Solved] External Display Flickering at High Refresh Rates on Mac Studio M2 Ultra: 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 Studio M2 Ultra: How to resolve DSC compression and VRR handshake failure over USB-C DisplayPort

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  • November 14, 2026 at 9:40 pm #12783
    Mason Schmidt
    Community Contributor
    Diagnostic Hardware Specs: Mac Studio M2 Ultra | OS Version: macOS Sonoma 14.7 | Archive Source: Apple Support Community #256229219

    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 0xc749 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) | Kawai MP11SE Stage Piano | AirPods Max | Raleigh, NC
    Classical Pianist & Spatial Audio Arranger | "Verified Apple Discussions Archive"
    November 14, 2026 at 9:40 pm #12784
    Dennis Edwards
    Community Contributor
    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.

    HomePod mini (Stereo Pair) | Apple TV 4K | iPad mini 7 (Wall Mounted) | Barcelona, ES
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