Help Learning Grid Interface? (not updating on scroll in designer)

Converting my site’s original layout to CSS grid and having some difficulty. The grid doesn’t update when I try to scroll within designer. The following screenshots demonstrate the behavior I’m experiencing when I attempt to scroll horizontally to the right.

I need to add content below the portrait to the far right, for example, but when scrolled, the grid doesn’t move and the gridlines disappear (presumably because that space is technically occupied by other content - see first screenshot).

This is my first time working with grid, so I’d just like to understand if I’m making a mistake. My images are HTML embeds (for the purpose of WebGL script) as opposed to native Webflow images. Not sure if this could be making a difference?

Thanks for any insight!