On the Products page, each tile showed the first photo uploaded for that product. When a product's back photo happened to be added before its front photo — sometimes by a fraction of a second within the same upload — the tile showed the back of the product. There was no way to influence it: the side you had set on a photo made no difference to the grid.
Tiles now prefer a product's front photo. If none of a product's photos is marked as the front, the tile keeps showing the oldest photo exactly as before, so nothing changes for products whose photos have not been categorised.
This also makes the "side of product" setting on the product page meaningful in the grid. If a tile shows the wrong side, changing that setting on the correct photo now updates the tile.
Separately, a small number of product tiles were loading the full-resolution original image instead of a thumbnail, which made the page slower to display than it needed to be. The missing thumbnails have been generated for every affected photo, and all tiles now load the smaller version.