Hi Andy,
I’m working on a MacBook Pro.
It surfaces in Chrome, Safari, Firefox and Opera.
It also happens on a different macBook Pro.
Reloading solves it for that page but going to a next archive page brings the problem back.
I can remember in the past when I was using de masonry scripts from DeSandro (https://masonry.desandro.com/) I had to load an eventie.js and an imagesLoaded.js script to get rid of this problem. I also do recall that you helped me before with a masonry issue for woocommerce: https://uxlthemes.com/forums/topic/masonry-sometimes-messed-up/
Can it be related?
On my iPad I don’t see it. Looks like it is macOs related or are you on a mac as well?
Adri