@Koen
It’s really weird, as the images are being cut-off by the bounding of the “Gallery Container”, if you turn off the “Overflow: hidden;” from the CSS, it’s displays all the photos, but I don’t think this will work on publish as then you’ll get a horrific side-scroll bar!!
It might be a bug!? As the settings you have applied are exactly like my build and I just went in to test the original and it works fine!?
I’m gonna have another play, if I work it out I’ll be sure to message!