Product Image Gallery is no longer a grid

My product images on the product pages have always shown as a grid under the main image. Yesterday I noticed that there is no longer a grid but a vertical line of images, all of which are blurry since they are blown up versions of the thumbnails. I regenerated the thumbnails, cleared every cache I could think of, disabled the store customizer, but no improvement. There are also some missing featured images scattered throughout the site — I don’t see a pattern.

Is the problem with the theme, woo commerce, the plugin or something else? I don’t even know where to start looking. It had been fine the last time I looked.

The page I need help with: [log in to see the link]