Not all picture files are showing in Pictures

I just installed Kodi on my Xbox so that I could play a slideshow of pictures from a USB. When I go into the app, I can see my USB under pictures and select the correct folder. But it is only showing 18 pictures in the folder, when there are 200.
If I go to File Manager, the USB appears, I can select the same folder and it shows that there are 200 pictures in the folder.
Why are only 18 showing in the folder under Pictures?