What steps did you take? Was there any errors after updating the forum?
Wiping all files and importing the database is unconventional. Did you run migrations during the update?
If the only errors are the fonts and missing avatars, you'll need the assets/fonts/ and assets/avatars directories restored from the original install. The former is only created during a install and user avatar uploads are kept in the latter directory. Do you have a backup of your original flarum directory?