[Plugin: FooBox] Only some pictures open in the lightbox, others don't work

Hello!

I have a small but annoying problem with the FooBox plugin / opening pictures, but I’m suspecting that it might be something more.

Some of the pictures open in the lightbox, others are “unclickable” and I’m not sure what’s causing the trouble – their settings seem to be the same.
After deactivating FooBox, the pictures that used to open in the lightbox open in a new window, while the ones that didn’t open still don’t open at all.

I’m not sure what causes seemingly random pictures, umm, unable to be clicked on.

Here’s an example: https://www.thecluelessabroad.com/overcoming-culture-shock-welcome-to-vietnam/ – the main, featured image doesn’t open in the lightbox, same goes for the second one. The third one and the fourth one work perfectly.

I’ll be grateful for any advice! ?? Thanks!