Disappearing image - lazy summaries grid block

Site URL: https://jackeames.com/instagram

Bit of a strange one...

I'm implementing Lazy Summaries on a client's website and it's working beautifully... apart from one weird thing. The gallery consists of around 80 images and one image in particular isn't appearing in the gallery despite being uploaded in the same way that all the other images were.

I've tried deleting the image and re-uploading it a couple of times, but no luck! Has anyone come across this before? It's image number 34 out of the entire gallery, so not even the most recent/oldest image. 

Wonder if this is some odd bug?

 Any suggestions greatly received!! 

Sammi x 

It's specifically something to do with the position of the image within the gallery as when I re-add the image so that it appears at the very bottom of the grid gallery, it shows up. SO WEIRD.

I managed to get the image to show up by adding the same image twice to the gallery and placing them next to one another.... but still super odd.