Ken Burns effect does not work on my iMovie

Sometimes my Ken Burns effect does not work. I set a start point and an endpoint for a photo that I placed on top of a video. When I check to see if it works, sometimes it doesn't work. The zooming doesn't happen. The effect just sits on the start point and doesn't zoom to the endpoint as the video plays.

I then go and try to tweak it. Sometimes the tweaking works to get it started, and sometimes it doesn't. I can't figure what gets it to work again or why it didn't work in the first place. Any ideas?

Thanks,

Pat M.

[Re-Titled by Moderator]

Original Title: Ken Burns Sometimes doesn't