I’m not sure how out of sync because Final Cut is not registering that it is out of sync. I transcoded the footage at 24fps and my former editor said that it was actually supposed to be 23.something and that this error might occasionally result in some synching issues. I have not noticed it with the exception of this one part.
However, the timeline issue has happened both in and outside of syncing issues. I will be playing something in the viewer and the sound will be fine, then it will either be muter or drastically lower in the timeline.
Just to let you know, my editor originally synched the footage with pluralEyes.