10bit C-log footage breaking when grading with Hue/Lum

Hi, I have switched to Final Cut Pro from DaVinci Resolve (Free version), as I have started shooting in 10bit 422 C-Log which the free version of DaVinci won't accept.

The whole point of switching to 10bit was so that I had better flexibility with adjusting the colours of the footage. However when I use Final Cuts Hue/Lum slider to raise the luminance of the yellows/oranges, the footage starts to break (the roll-off between colours is harsh and pixelated), as if it was 8bit footage or even less.

I've tried with plain 8bit footage and still have the same issue.

I never had this problem in DaVinci even with the luminance value maxed out, so I'm wondering if maybe I'm not importing the footage correctly or some how Final Cut is automatically lowering the resolution. But I check all the optimised/proxy settings and it's telling me I should be seeing the raw 10bit footage.

Would love a bit of help, thanks.

Any footage will eventually break, but that does look abnormal. I'm not familiar with Canon files, but try importing the footage using "copy to library". If you imported using "leave files in place" or copied the files outside of the original folder tree before importing, it's possible some of the color metadata in sidecar files wasn't used.

Also verify you have the latest version of Apple Pro Video Formats installed. That is part of MacOS and is updated in System Preferences>Software Update. 

You can check the version in About this Mac>System Report>Software>Installations, scroll down to Pro Video Formats. The current version is 2.2.2.

If that doesn't help, please state the version of FCP and MacOS.