I'm not making this up and not hallucinating
I've got an album with images missing and trying to figure it all out. I'm looking at a "master" (an old site of mine); FTP filenames within ZP album structure and Thumbnail page of the same album in ZP to help find what images I missed uploading. Thought be viewing thumbnails, I'd spot missing pics.
I took the same picture twice and uploaded both as 9601-003 and 9601-003a respectively. I hovered over to ascertain the filename and one shows as 9601-003 the next as 9601-003a, as they should. When I hover over the next image it claims to be 9601-004, the identical view of -003 and -003a. However THAT IS NOT correct. In FTP view, the correct image of 9601-004 is the next image in sequence of the album.
In otherwords, I've got an extra thumbnail of an image that isn't in the FTP directory with the number it claims to be. I don't expect you to be able to replicate this! However, no idea how to fix. The real 9601-004 shows in Thumbnail as 9601-005 and subsequent thumbnails follow, all one number out.
Comments
Maybe one of the images you miss is either set to unpublished or maybe corrupt.