Hey Christina,
Thanks for reaching out!
If simply changing the theme caused the change in display, then your current theme is likely the culprit here in one of two ways: first, the theme could be pulling in image sizes of a smaller sizes or with different cropping configurations; or it could just be handling the images differently with its CSS.
There could also be some combination of these things.
I also noticed that the image src attributes are quite unique, and are using an array of sizes as shown in this screenshot:

That’s not something our plugins do, so it could be another issue arising from your theme or possibly another plugin on your site.
I would recommend reaching out to your theme author for some insight on the size changes that arose after you activated that themeāI hope they can shed some light on the issues!
Thanks,
George