I’ve been getting the exact same error, Online Arsenal Community Fan Forum when clicking on either avatar, on a mac, happening in Safari, Chrome, Firefox, logged in or logged out.
It’s happening on the user preferences/messages screen too, completely wiping the content of the page out once I’ve set the birthday (though it may just be because the birthday is today? - edit: just got someone else to check and they can access their messages/preferences when their birthday is set NOT to today).
The emoji works fine by the way, if you go into a topic that the person has used then it’s there Planned Maintenance - Announcements - Online Arsenal Community Fan Forum
I don’t know much about the discourse core and how it reads files so forgive my ignorance, but I’d guess from that error message and this commit that discourse/helpers/fa-icons has moved to discourse-common so the path may be wrong?