Incorrect Font Change Mystery

Could anyone help me understand why the fonts on my published website have all gone “basic”, no matter which browser I look at them with, when in the Editor they still look exactly as they were originally designed (and how I want them to look)?

The site has been published and looking fine until a couple of weeks ago, absolutely no changes to the site have been made for months (unless webflow have done something), the fonts that are supposed to display are still there in the Editor.

I tried republishing and still the Editor version is different from the published version only when it comes to fonts. Everything else is fine.

What has happened? What can I do about it? Any help greatly appreciated.