There is no direct correlation between the thumbnails and the electronic file.

You may start with a match like if you import a PDF and generate pages, but if you start making changes to the pages it won't change the PDF that's still attached.

The thumbnails represent the individual pages of the native Laserfiche document, which technically doesn't even have to be the same document as the attached electronic file.

Basically, what you're seeing is that there are pages added to the (native) document, and there could be any number of reasons for that, but the attached PDF would need to be regenerated to match those changes.