Well, of all the gallery styles (vertical, grid, slideshow, carousel), you have selected to use a "vertical" layout as in this example
https://demo.photo.gallery/galleries/landscapes/, and additionally you have set the gallery to "wide". This is a gallery page, so how exactly do you want it to display? How about trying the "grid" layout as as you have in your other galleries like this one?
http://www.merelyafleshwound.com/skiing ... -mountain/
How exactly were you expecting to have the image display with those settings? X3 is a "responsive" gallery where images are not strictly measured by the pixel, but will scale to fill the space available, especially when you are using the vertical scroll in "wide" modus with no grid.
The reason it displays correctly in the popup window, is because the popup window is created specifically to display a single image, will not scale the image above its original size, and can easily center the image. In a gallery layout with the default vertical style, it will scale the image to the containers width, which you have set to wide. What are you trying to do anyway?