Featured image resizing issue

Hi, After I applied an update to the Clean Journal theme all the featured images have assumed their actual file dimensions and do not cover the width of the 'site' anymore as they used to. Well, I say all, the home page featured image is fine, it's just the featured image on all other pages. Their file size is around 1000px x 600x and all images are aligned left as well, leaving an odd-looking blank area to the right of the image. Has anybody else come across this issue and is there a css fix that will work? The website in question is https://www.treeprofiles.co.uk/ Thank you, Glenn