I just updated to FCPX and I am having a recurrent issue (see the photo).
The glitch appears mostly at the beginning or at the end of any clip for a fraction of second after I did basic grading with color and exposure. When the glitch appears if I alter the grading, let's say, moving the -19 exposure to -18, the glitch disappear, even if I return the exposure to -19 again.
It is if like the glitch tends to mix two footages together, the end of one with the beginning of the other.
Not sure if related, but the red color flickers in all the footages.
I have FCPX installed in a MacBook Pro with macOS High Sirerra 10.13.6 and I working Sony footage with Cine4 profile.