I've been using the Chrome browser on a 13" Macbook and I experience it in all galleries. I just tried it on my Mac desktop with a large display and everything is fine.
I guess it has to do with the fact that the whole page doesn't show on the Macbook and each time I click on a photo it goes to a new page and only shows the top section.
I usually don't have this issue on other sites such as Facebook, Craigslist, RV Trader, etc. With those, the photo stays centered when I go from one to the next.
I wonder if this is unique to Macbooks or if other laptops have the same issue. Maybe you can try it on a similar Macbook.
Thanks for getting back to me so quickly.
2002 Itasca Suncruiser 35U