When trying to delete a menu link via the "Delete"-link in admin/structure/menu/item/x/edit i get an error message:
Uncaught PHP Exception InvalidArgumentException: "The URI "base:///admin/structure/menu/manage/main" is invalid. You must use a valid URI scheme. Use base:// for a path, e.g., to a Drupal file that needs the base path. Do not use this for internal paths controlled by Drupal." at /var/www/xxx/core/lib/Drupal/Core/Url.php line 207
It seems to me that link for deleting the item is somehow causing this error. The link looks like this: /admin/structure/menu/item/2/delete?destination=%2Fadmin%2Fstructure%2Fmenu%2Fmanage%2Fmain. If I remove the first slash and take the link this /admin/structure/menu/item/2/delete?destination=admin%2Fstructure%2Fmenu%2Fmanage%2Fmain it works. But on the edit form the same destination is working.