If you try to figure out why your Oxygen Gallery is not lazy loading like you expect, try this tutorial. Hope it helps you! In my tutorial will be masonry gallery rebuild to 1:1 square gallery. Are you looking for masonry gallery? The main thing is changing the rule of loading images and never use Flex gallery.
Many thanks to Alexander Buzmakov from Official Oxygen User Group on facebook who comes with this idea.
Gallery type Masonry vs. Flexbox
Always use Masonry Gallery. If you use the Flex gallery, Oxygen starts to generate images from the gallery as a background for < figure > elements.
Lazyload plugin which plays well with Oxygen
I tried lot of lazyload solutions – WP Rocket, A3 Lazy Load, Autoptimize lazy load, jQuery.Lazy and others. Best working for me is Flying Images by WP Speed Matters and WP Rocket.
Changing the way Oxygen masonry gallery loads
When you refresh the page now, you will see, that masonry gallery loads column by column. So the lazy load do nothing here, because all images are being loaded automatically. So we need to load the gallery same as flex columns in flex row.
You can play with the CSS to make your own layout. But you will need this definitely for Main gallery container.