Gray rectangles in place of photos
After converting my iPhoto library to Photos in 10.10.3, In the Photos view, I see lots of my photos, but I also see a lot of gray "placeholder" rectangles that look like there should be a photo, but the image isn't there. It seems like maybe there's metadata for a photo, but not the photo itself.
Anyone know what there are, and if there might be images that can be recovered -- or if there's a way for the system to clean them up?
Thanks,
Peter