It seems that Mapkit.js' hybrid map is returning 404 for the entire US mid-west at lower zoom levels. Grand Canyon National Park being an example. A quick cursory test shows that this affects large swathes of territories, as far noth as British Columbia and as far east as Maine.
Not sure when this started happening.
So what’s your question? Was this data available before? Is it available from the Maps app? Maps really aren’t Apple’s focus.