We've done a simple Google Sites and changed some fonts to Montserrat and Helvetica Neue. These fonts display perfectly on the sites.google.com/view/mysite page, as you can see below:
However, when using a (previously set up) custom domain to access the website, fonts change to Times New Roman everywhere. I don't have a clue why. HTML code is the same between both websites so we don't know what's going on. If someone is able to guide us a bit, it´d be very appreciated