This happens when you do not upload the accesslinks file in the .well-known folder. Please see step 1 in this video : https://youtu.be/8QkRH3yE6Hg?t=80
Add following CSS in customizer - Custom CSS
in WP Admin - Vibebp - Settings - Service Worker - Precache resources. While saving make sure you regenerate service worker with an updated version.
IF above does not work, another alternate is to edit the H5P plugin and add the font definition. This can be done via cpanel or FTP. Refer following screenshot for reference.