Grey boxes appearing in Lightroom
I have grey boxes appearing in my Lightroom as you can see in the picture below.
I saw lots of questions where every box was grey but for me out of thousands of pictures only a hundred or so are grey. I recently made a lot of changes in my catalog when I merged my backups and somehow this happened. I don't think any of my photos are missing (although I could be wrong), I just want these boxes to go away.
I can look at the grey boxes in either the loupe or grid view. I wanted to see what file they were associated with so I right-clicked on the box, but nothing happens. I'm not able to pull up a menu like I am when I right-click an image. I thought I should synchronize my folder to get rid of it, but I noticed they're not actually in any folder. When I click on my folder, they disappear. Then I noticed that there are more photographs in "All Photographs" under the Catalog section than in my folder in the folder section (see picture).

I also tried marked them all as rejected and then deleting them, but nothing happens when I do that. I don't know what else to try to get rid of them. Any ideas?
