Catalogue images, scrolls and theme sizes
Check the concrete gallery and list implementation of the theme. A global lazy loading module should not unnecessarily delay the first visible main image.
Check the role of the image in the product as well as the size requested by the theme. A correct original can still be loaded too large or distorted by incorrect thumbnail selection or inappropriate gallery output.
Where to check the setting in Magento
Under Images and Videos, check the scrolls of the product and the output in the active theme. Compare the file loaded in the browser with the intended role and size. Variants and Store Views may use other media or captions.
Example of this specific finding
Illustrative control case: Twenty images far below the first visible area load immediately. The large visible hero image, on the other hand, does not belong in the same delay rule.
follow-up audit in Magento
Test product listing, main image and zoom separately. After a variation or image change, also check the actually used cache/media URLs.
Suitable downstream images are loaded delayed and checked in the network protocol when scrolling. Continue to request visible key images in time.
Derogations and scope
Lack of lazy loading on the LCP image is often intentional. A blanket rule for all images can worsen the visible loading time.
Reference: Magento Open Source or Adobe Commerce with classic storefront. Consider store views and extensions; other storefront architectures have their own configurations.
Classify the general error
Definition, system-independent causes and further correction examples: Judge images by their position in the first screen