Ok, I've got a very simple set up with a very frustrating problem.
I'm doing several intro graphics, all the same way. There is a text title, larger font. Then below a text subtitle, smaller text. Both texts have the opacity key framed to fade in and fade out at the end. The subtitle text has an effect bringing it in (so actually I can take off the fade in on that one - I have tried both ways).
The problem occurs within the Final Cut timeline. When I play it in Motion, everything is perfectly smooth. When in Final Cut, after the end of the text effect bringing in the subtitle, within a few frames after the animated text is finished, both Title and Subtitle twitch one time.
OH MAN!! It sounds so strange to complain about, but it's driving me crazy! I have been able to fix SOME of them, by going into the keyframe editor, and moving keyframes of both Title and Subtitle to be the same upon fadein and fadeout, and on some of them it seemed to fix it. But, on some others, I just can't get it to quit. Sometimes the twitch will even change to a different frame. It always seems that there are NO CHANGES with key frames or animations where the twitch occurs. That's what boggles me. Any ideas?
Don't key frame a fade in and fad out, use the Basic Motion, Fade In/Fade Out Behavior, it's a lot faster. In FCP, I've had that nasty twitch happen before, dump the render files for the clip (motion project file) by lowering the opacity and then raising it back up or something and then re-render it. It's worked for me every time.