The source of the problem is most likely the fact that you're using a Trial version of FCP.

Final Cut Pro Trial, contrary to popular belief, is not simply a time-limited full version - there are a few areas in which the Trial is not working properly (unlike the full official build). Unfortunately, Apple doesn't mention anywhere what the exact differences are and therefore we can not officially support it.

Additionally, we wouldn't recommend using the trial version of Final Cut for any professional work - there's no guarantee that the app won't crash/interfere with your project at some random point. Aside from that, you may also experience performance and stability issues that may affect your workflow.