Not using scaled images

I am not sure if this is a problem with the theme or with WordPress in general or benchmarking sites, but if this is the wrong place I hope someone can point me in the right direction.
I am trying to get my site https://www.svenskarecept.se a better ranking and better speed, but when I use for example GTmetrix the score is bad because of the recommendation Serve Scaled Images pointing to a lot of images with “… is resized in HTML or CSS from 520×347 to 239×160” and “… is resized in HTML or CSS from 390×260 to 169×113”. I have used the plugin Simple Image Sizes (https://www.ads-software.com/plugins/simple-image-sizes/) the create those two sizes, and looking with FTP the sizes are present along with all the other sizes.
So my problem/question is why Oria, or my child theme for that matter, does not use those image sizes but continue to resize bitter images? Are those sizes hard coded into a html och css file somewhere and removing that will make everything work, or what am I missing?

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