It does the same for me. Found that it somehow width of the media is set to 21%. For me placing this in de the products css helped:
.page-template-template-fullwidth-php .site-main ul.products.columns-4 li.product, .page-template-template-fullwidth-php .header-widget-region ul.products.columns-4 li.product, .page-template-template-homepage-php .site-main ul.products.columns-4 li.product, .page-template-template-homepage-php .header-widget-region ul.products.columns-4 li.product, .storefront-full-width-content .site-main ul.products.columns-4 li.product, .storefront-full-width-content .header-widget-region ul.products.columns-4 li.product {
width: 100%
}
Let me know if you found another fix tho!
