A quick update.
It is partially a workaround since is not a true “fix”, but I will stick to this solution and explain it here for those who are interested.
I disabled “page transitions” under theme options -> general options.
This removes the issue of loading animation until full loading, and overall enhances A LOT the perceived website speed. If anyone is using Cardinal with image-heavy websites, I suggest to disable page transitions too, even though they look good.
The “I’d like next images to load as I scroll down the page” is solved thanks to “lazy load” WP plugins, but I’m not sure if I will implement it.
Hope someone will find these informations useful.