Why does magento 2 throw an address error at the step of submitting an order?

Question

Magento

Hit again like chickens in the pluck. The former figures have done a lot of harm - now I'm going crazy. The problem is the following - all addresses are poked out - only pickup and delivery to the post office is used. With an anonymous customer, everything is fine - orders go away. But, it's worth going through Facebook and trying to send an order, then at the last step - on the Send order button - a sign "Check shipping address information" suddenly pops up and lists what is missing there. Naturally, the order is not sent. Hence the question: where to look for this check? Checkout and Customer combed up and down - there is no such check. Where else to look? Already a man-shift killed in search and nothing!

Answer 1

Found this test myself. "Expected" ended up in sales/model/service/quote.php. "I love" magento for code clarity and order! And also for community.