PenciDesign replied
Hi,
Yeah, because Justified gallery will need to follow a fixed height you've set on Customize > Single Post Options > Custom the height of images on gallery images (unit is pixel)
That why some images aren't not fit with the screen like your case.
If your gallery is not much images, I recommend you use it as grid gallery style or masonry style... Because all justified gallery need to fit based on the height...
You can see this issue appears with the Justified gallery library also here:
http://miromannino.github.io/Justified-Gallery/getting-started/
Best Regards,
PenciDesign