Photos not showing in preview

Hi, I am knew to this forum and indeed FCP. I can import my photos to see them on time line. When I run not all photos appear in the preview i.e I have a blank screen and it moves to the next and so on. Some photos do appear and some don't. I;ve resized photos to try solve it, I've reset preferences all to no avail.
Wonder has anybpdy else had this problem?

Make sure your photos are JPEG or PNG and that they're not super huge.
Maybe try trashing all the render files for that Library.