I have recently tried to change my favicon from the default NodeBB one to something my personal to my forum. After the upload and confirmation the changes do not happen and the default NodeBB favicon remains.
@Scuzz if you use the imgur plugin, it doesn't allow ISO files which is an issue. I ended up logging in to my hosting using FTP and put the fav icon into public/ then overwrote the old one. Works just as well.
AFAIK we always upload the favicon locally because imgur doesn't allow ico files, you probably need to restart the forum too since express caches the favicon too.