Letter-spacing issue on mobile for custom <h1> (Fulton in SS 7.1)

Using the Fulton template. I've added several typefaces to my site and defined all styles in my custom CSS. Per page, I'm either using the default squarespace text box to add copy, or I'm adding a code box and just adding a little bit of CSS to my html text to change color or alignment.

I'm not having trouble anywhere except my <h1> is showing up weirdly on mobile—for some reason seems like letter-spacing is being added. It doesn't show up when I manually resize the window on desktop, just on mobile (see attached). I don't have any manual letter-spacing added anywhere on the site via CSS, and I also don't have any letter-spacing added to any of my text in the squarespace site styles dialogue. 

Anyone have any idea what could be causing this? Site is dustlight.co and the pass is dusty if you want to check the backend.