Per T157145#6858470, when page image thumbnails are greater than 300kb they will be ignored by Whatsapp when a Wikipedia article is shared appearing like so:
PageImages should therefore consider the size of the thumbnail when choosing a page image or adding the og:image tag to the page.
- Go to whatsapp
- Paste a link to a wikipedia article that has an image
Expected: image preview should appear within whatsapp
QA Results - Beta