Lazy-Load Not Working on Galleries

So initially I thought the last solution in this forum might have fixed the problem:

https://kriesi.at/support/topic/lazy-load-not-working-on-blog-gallery-or-portfolio-item-images/

but I’m working on a masonry gallery at the address linked in private content and there’s no hint of lazy loading going on in the network panel in the chrome console.

The last solution offered was to default images to lazy-load via this code added to functions.php:

function handler_wp_img_tag_add_loading_attr_mod( $attr_value, $image_tag = '', $context = '' ) 
{
	return 'lazy';
}
add_filter( 'wp_img_tag_add_loading_attr', 'handler_wp_img_tag_add_loading_attr_mod', 9999, 3 );