Hi there,
Are you sure you set it to 1200px? The code is still displaying the 300x300
<img width="300" height="300" src="https://www.thehummingbirdlodge.com/wp-content/uploads/2018/04/Embodying-Module-1-300x300.jpg" class="attachment-shop_catalog size-shop_catalog wp-post-image" alt="">
Have you tried installing Force Regenerate thumbnails plugin and regenerate them? Changing image size will only take effect to newly added images, existing will remain on its size.
And please provide your site’s login credentials so we could test it too. The size is being pulled from Woocommerce setting and not from the theme (shop_catalog).
Thanks!