We’re aware of an issue with FilmConvert Nitrate and the new Final Cut Pro 10.5.2 update and are working on a fix for it now. We don’t have an ETA for the resolution at the moment, but we will let you know as soon as it’s available.
In the meantime, there is a workaround you can use to open your projects graded with the FilmConvert Nitrate plugin. Please see the instructions below:
Launch Final Cut Pro in compatibility mode by entering the following command in the Terminal.
screen -d -m arch -x86_64 /Applications/Final\ Cut\ Pro.app/Contents/MacOS/Final\ Cut\ Pro