Final Cut Pro: May Stop Responding When Connecting Offline Media Clip
If you open a media clip that is already in use in Final Cut Pro with another application, either application may stop responding or "freeze" when you reconnect the clip in Final Cut Pro.
Symptom
Final Cut Pro stops responding or "freezes" when you reconnect a media clip that was opened with another program.
Solution
Close the media clip in the other program before reconnecting it in Final Cut Pro.