I've recently encountered an issue importing images into iMovie 10 on some of our computers. The machines are running High Sierra and iMovie 10.1.6.
On effected units, some imported images appear as a black box with a small portion of the image appearing in the upper left corner of the box. On other (apparently identical) machines, the same image imports with no issues.
The problem occurs in all user accounts on the effected machines, even a newly created user, so preference or Movie Library issues seem to be ruled out. The only fix that has worked so far was a full OS and iMovie reinstall.
Has anyone else encountered this? If so, were you able to find the cause?
EDIT: upgrading to Mojave does solves the issue, but this is not a practical solution in our situation