This is because the last product image is taller.
I do not remember what product media settings were available for Dawn 2.4.
However, you can manually force images to fit into square – when configuring “Product information” section in Customize, open “Custom CSS” at the bottom of the section settings and paste this code:
.product__media {
padding-top: 100% !important;
}
.product__media img {
object-fit: contain;
}
Before => After

