There seem to be no JS error when I checked on the console and I can't see any code that should be added when you set a font family for the headers and body font.
Would you mind testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it's fixed, you'll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time. Also, kindly make sure that you have everything up to date including the plugins in case the plugin conflict check does not work.
If the issue persists, please provide us with the admin logins of your site in a Secure Note so that we could check this further.