Why are featured images sometimes cropped, and sometimes not

I am developing a website using Wordpress CMS, in particular Hatch theme. I noticed that in some posts, featured image is displayed full size (like here) but in others, featured image has a smaller size, cropping the original image, I don't think it is about image starting size, because some of the images displayed correctly are way bigger than the one it shows as cropped. Both of them are made with cameras. Moreover, if I change the freshly updated photo with another one that i recently uploaded, it shows as cropped, while changing it with older photos shows it full size

Do you know why it behaves like this, and how I can fix it? Can it be an extension issue (even though they both are JPEGs)?

Thanks