Hi,
When an iMovie exhibits unexpected behavior sometimes a simple deleting/resetting of preferences can cure the problem.
To delete/reset preferences open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new empty library. Reopen your old library to get back to your projects. (To reopen your old library close iMovie and go to your Movie folder or wherever you have your old iMovie library stored. Double click on the library’s icon. iMovie will open in that library.) Now see if the Ken Burns feature will function properly on playback. Possibly you may need to reboot to set the changes. Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.
Another thing that you can try is to copy your media to a newly created project and see if that cures the issue. To copy a project's media to another project, do an Edit/Select All, Edit/Copy, and then go to the new project and do an Edit/Paste of the media into the timeline. Your edits will carry over.
-- Rich
