This site has a messed up nav because you’ve added Font Awesome class to the Custom Classes fields: http://unser-quartier.de/
If you remove the “fa-mortar-board” and fa-lin classes, it will be fixed.
Those classes should be applied to
<i> elements within the navigation menu item, not to the item itself.
Any chance we can fire up the update on the other site again so I can take a look personally?