Hi, that is strange. There is an open issue related to only getting a quarter of a zoomed product image on at least one site. Maybe it is a related problem? Feel free to add example URLs to the open issue at https://github.com/jscher2000/Save-webP-as-extension/issues/10 (or you can email me at jscher2000@outlook.com if you don't want to create a Github account).
Meanwhile, does it work any better if you open the image in a new tab before trying to convert?
