iMovie video selection fragmented

Hi there,

I have been using iMovie to make a video and have noticed that when trying to select portion of a video the yellow outer line that shows the selection seems to all over the place. I have inserted 2 images below, the first showing how it has normally looked and the second image showing what is happening now. I have tried multiple videos, some of which I have used in the past with no drama and yet they all seem to be now having this problem. It is making very hard to select the exaction portion of video I need so if anyone can help determine whats going on that would be great. Thanks