Final Cut V 10.6.6 messed up previous audio effects

One idea I had was maybe exporting an XML of the project and seeing if the audio settings are in there but I haven't had time to try that yet. I think you saw but I mention the bug here Channel EQ and Limiter broken after 10.6.… - Apple Community and posted a .gif of just how messed up this bug is.

Definitely send Apple feedback about this super bad bug if you have a moment. Feedback - Final Cut Pro - Apple and if you can send them links to our discussion here.

I have heard many reports similar to yours. There are lots of audio issues with FCP 10.6.6. There are reports of changed plugins, missing plugins, and ones that don't work as expected.

In a few cases, people have specifically mentioned having to remove and re-apply their saved presets. This seems to have worked for them. You might want to double-check that the plugins you used to create your preset(s) are still listed/available, as well. At least one person has reported not having the Limiter plugin anymore.

The larger lesson here relates to managing FCP and various projects, in general. It's a good idea to turn off all automatic updates, so that things don't change and affect any work-in-progress. Compress the FCP application whenever a new version comes out and keep that around in case you'd like to move back to an older version. Of course, it's a "best practice" to never upgrade/update anything while you're involved with a project. It's a good idea to wait whenever macOS or FCP are updated, in order to see if there are reports of issues here or on places like fcp.co. Having a spare, external boot drive that you can use for testing is a way to see if new versions of macOS and FCP will work for you.

same issue here it's a joke, and I only use apple audio plug ins but by saved compressor and limiter set up does not work anymore