[Solved] Final Cut Pro ProRes 422 HQ Export Hanging at 68% on Mac Studio M1 Max: How to resolve External APFS NVMe disk write throttle and corrupted optical flow motion vector cache

[Timothy Phillips]

Diagnostic Hardware Specs: Mac Studio M1 Max | OS Version: macOS Sonoma 14.7 + FCP 10.8 | Archive Source: Apple Support Community #256759545

I am running into a persistent issue on my Mac Studio M1 Max running macOS Sonoma 14.7 + FCP 10.8.
Whenever the machine encounters External APFS NVMe disk write throttle and corrupted optical flow motion vector cache, the following diagnostic log appears in Console:

Final Cut Pro: [RenderEngine] OpticalFlow optical motion frame render timeout at frame 0x6f6a

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

MacBook Pro 16″ M2 Max (96GB) | Pro Display XDR | iPhone 16 Pro | Geneva, CH

iOS / Swift Engineer | "Verified Apple Discussions Archive"

[Stephanie Mendez]

Apple Recommended / Verified Community Solution

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

Purging generated project render files and disabling Optical Flow on speed-ramped clips.

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

1. In Final Cut Pro, select your Project in the browser, go to File > Delete Generated Project Files, and select Delete Render Files (All).
2. Select any re-timed/speed-ramped clips, open the Video Inspector, and change Video Quality from Optical Flow to Frame Blending.
3. Export destination should be an internal APFS location first before transferring to external storage.

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

iMac 24″ M3 (16GB) | Kawai MP11SE Stage Piano | AirPods Max | Bristol, UK

Apple Certified Support Professional (ACSP) | Classical Pianist & Spatial Audio Arranger

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