Galllery doesn't display side-by-side images

Hi

I have had 2 galleries on one page since I created the site using this theme without an issue. This morning, when I have gone to make changes to fonts used on the site, the galleries do not display properly (I haven’t changed them!).

There are three images on each gallery that are side by side. I had them pop (the animation effect) when the user reaches them (temporarily disabled due to this issue). The images now are displaying one above the other, which doesn’t work, making the page look awful.

How can I fix whatever has broken? If I know what had changed to make this happen, I’d have an idea of where to start ;-)

Thanks

Steve