scrollbars beneath tiled gallery

Hi,

for some reason all of a sudden there are appearing scrollbars beneath the tiled gallery, which makes it look like this: https://img.photobucket.com/albums/v422/kittykittylamb/various/scrollbar.jpg
It partly covers up the captions aswell. When I switch templates or update the image gallery the same problem occurs, or if it doesn’t the first time, afer refreshing the page it will. I read somewhere else it could have to do with the theme’s CSS and the “small” class used in Jetpack, howeer to my knowledge nor my style.css or Jetpack itself have been modified. Even so, whatever happened, any ideas on how to fix this? I’m using the Book Lite template, by the way.

https://www.ads-software.com/extend/plugins/slimjetpack/