How do I edit clip in iMovie to correct an issue?

Made a little storyboard film under trip title about 1 1/2 mins long. All good but wanted to make one last edit snd suddenly it stopped editing during clip and now I have a big blur where that clip is! It’s as though everything is jammed. When I press edit absolutely everything is jammed. I have to switch my phone off to get rid of it. The film still plays but with the big empty blur!

[Re-Titled by Moderator]