The Uncode theme seems to have similar issues (due to using megamenu in same way) as well. This line seems to be the problematic one:
wp-content/themes/uncode/core/inc/edit_custom_walker.php:197
If you change it to this:
do_action( 'wp_nav_menu_item_custom_fields', $item_id, $item, $depth, $args, $parent_mega);
the problems disappear. Does look a bit shady to me, though. If you have a better solution it would be very welcome.
