So, the last time I worked with this theme, I thought it was set up to have uniform gallery image sizes (though sometimes an odd image would get squished instead of just cropped, and I’m not sure why that was). I’m running into the same issue here and am wondering how to fix it (and if I can just fix it in the child theme CSS or, if not in the CSS, can it still be done via the child theme so as not to mess with the core theme files?
Also, out of curiosity, is there a way to add intro text to individual gallery categories? In other words, when “All” is selected, no intro text appears, of course. But if an individual category is selected, in addition to the images switching around all nifty-like, a line of text would appear at the top of the grid? This may be too much customization to be reasonable, but I just thought I’d ask in case 🙂
WordPress algorithm for looking for an image of a certain size has some condition checks which does not always result in finding the image of right size. I have had issues before with it. But in your case, I see an image of size 400×400 which is a loner since other images do not have a image with this size and theme does not support 400×400.