Phantom Audio clips becoming invisible on timeline--but still play

fcpx-10.0.5

Yesterday i was editing a project and suddenly some audio clips from one event file became invisible on the timeline screen. The clips continued to be audible on playback, but some disappeared from view. Occasionally they would reappear when I navigated back and forth. But then others would disappear. The audio is an aiff narration file with many edits--some of which are only a few seconds in length.

I don't seem to have lost any content. But it is mysterious and disconcerting. Has anyone else expeienced this phenomenon?

Thanks!

Carroll