Theme looks different when served from its build directory compared to another website

I have made a Jekyll theme, jekyll-theme-dusk. It is available on rubygems. Whenever I serve the theme locally, it works fine, with all the footers and navigation working as intended, but when I add the gem to my website, and then serve that locally, suddenly, the homepage has the footer and the navigation missing, even though the file for the navigation (_data/navigation.yml) exists. Can someone help. It is worth noting that the theme is built with GitHub pages in mind, but that I haven’t tested the website online yet.

I have just deployed my website online, and for some reason, the website has the home page working. However, the home page still does not work offline.

so it works fine deployed online but locally you still have an issue if the theme is loaded as a gem?

I’m not able to help with theme stuff, never used them. If you can post a link to the theme repo and your site repo that uses the theme maybe someone can help.

Yes, exactly what is happening, which is really weird.
The theme is at GitHub - Parmjot-Singh/jekyll-theme-dusk: i definitely didnt delete this repo on accident
And the website is at GitHub - Parmjot-Singh/ My Website......