When a promo code is added on the cart page, a preview thumbnail gets loaded into the product thumbnail as the page reloads (from the promo being added).The product thumbnail stays blurry because there is no scrolling on cart page. How to disable lazy loading on cart / checkout page?
Please make the full backup of your site and check the issue on the Storefront theme to detect if our theme causes the problem. Storefront is a free theme developed by WooСommerce.
Please, provide your site admin access (insert the site credentials into the Private content block under the message area) and confirm the permission for plugins deactivation, switching to the parent or default theme. This testing may take up to 15 minutes. You would better make the full backup of your site.
In addition, please provide the product page URL with the problem.