I just updated Wpforo (v 1.9.9) and Wordpress (5.8).
After that, all icons in the User profile & notification widget disappeared and were replaced by a code, see attached screen capture.
Thanks for your help!
This is not related to wpForo update. Somehow, the Font-Awesome CSS is not loading on your website. It seems WordPress 5.8 has disabled your theme Font-Awesome lib.
First go to Forums > Settings > Features Tab and make sure the "Enable wpForo Font-Awesome Lib" option is enabled, set it [sitewide] if you use this widget sitewide, otherwise set it [forum].
Then delete all caches, purge all optimizer and minifier plugins cache, purge CDN cache if you have. Go to forum front-end and press Ctrl+F5 to reset the browser cache.