If you try to add custom linkAttribute classes to the UI Menu, you will probably not see your custom classes in the link generated.
This is caused by this lines
First Level menu: https://github.com/ezsystems/ezplatform-admin-ui/blob/master/src/bundle/Resources/views/parts/menu/top_menu.html.twig#L25

Second Level menu: https://github.com/ezsystems/ezplatform-admin-ui/blob/master/src/bundle/Resources/views/parts/menu/top_menu_2nd_level.html.twig#L30

Custom added classes are not taken into account.