Thanks for your reply.
Yes, turning off Masonry has definitely fixed the issue. The reason I originally turned Masonry on was not so much for the look, but because another issue I was having seemed to be fixed by having Masonry switched on. It’s obviously not a major issue, but on mobile, if the page loads in portrait mode, the featured images don’t seem to expand to fill the container if you turn the device to landscape mode. Would I need a larger image size to make sure they expand (current 900 px), or is there a code snippet I could add to force them to expand?
I hope that makes sense.