It's probably the cover of the photo set which is on a different host than the original photo set.
Let's say you add a link with 27 images. The cover image (1) is on imx.to, photo set (26) is on vipr.im. If that cover image is deleted from imx.to for some reason, ripper will get 26 images from vipr.im but can't get 1 image from imx.to. This gives you that 26/27 screenshots.
Just check the set title. Most of them have the image count information like (x26+cover) or (x26) in the title. You can delete that post from the ripper if downloaded photo count matches the set title.
No it is not. Giving a like and downloading images are different processes.