That’s a result of the updated header.php I gave you for your webtrees theme, to fix the login / html block problem you had.
It is an unfortunate inevitability from using replacement file between releases. They often contain other changes that need further changes in sometimes many other files.
However, in this case you can easily fix it manually. In your file /themes/webtrees/header.php, in line 123 replace the string “fa-bars” with “icon-widget”.
(Note for anyone else reading this – no-one except Ron has been given this version of this file, so no-one else will have this issue)