Only thumbnails are indexed by google

Hi,
Like I guess many wordpress users, I use thumbnails in my posts to save bandwith. These thumbnails link to the original (unresized but losslessy optimized). I also use two sitemaps (images and normal one). I use a lazy loader (in W3 Total Cache)

For months, I’ve noticed that google images doesn’t index my images. Tried to figure out why, made several experiments (deactivated lazy load, changed the linking from the thumbnails to a media page instead, used structured data plugins, etc), but nothing changed. Zhe only images indexed by google are… the comment avatars!

Today I noticed in the google search console that the bot doesn’t check the fullsize pictures. Only the thumbnails.

So my question is, is there any wordpress user that utilizes thumbnails who get the full pictures indexed?

A second question: is there any way to resize through img html tags instead of providing thumbnails? Would obviously increase the loading time, but I guess it would allow my images to get indexed by google…

Thanks for any hints!

The page I need help with: [log in to see the link]