This has been something that has been bugging me for a while.
The Appearance -> Menus in Pro is incredible slow and almost impossible to use especially as a menu grows.
Currently have a site with a large menu and I keep having to switch to another theme so I can edit the menu.
As soon as I switch away from Pro the menu section is snappy and response and easy to work with.
While on Pro the menu is nearly impossible to use.
This does not happen if I switch to a different theme.
What I have done is set the below which also resolves the issue but this obviously means we can’t select icons for the menu items.
add_filter("cs_use_custom_fields_map", "__return_false");