This sounds like a macOS Preview compatibility issue with your specific RAW format. A few things to try:
- First, check if the issue persists in other apps like Photos or Adobe Bridge - this will help determine if it's a system-wide problem or just Preview.
- Make sure you're running the latest macOS version, as Apple regularly adds RAW support for new cameras.
- Try resetting Preview's cache by running this Terminal command:
rm -rf ~/Library/Caches/com.apple.Preview
If you're still having issues and suspect file corruption, you might want to try a repair tool like 4DDiG File Repair. I've used it successfully for problematic RAW files before - it can handle CR2, NEF, ARW and other RAW formats while preserving metadata.
Alternatively, you could try converting the files to DNG format using Adobe's free DNG Converter, which often fixes compatibility issues.
Let me know if any of these solutions work for you!